View Full Version : Ammonium Dichromate replacement for Carbon printing
The toxicity of ammonium dichromate puts a bit of a potential damper on carbon and gum printing, especially if one want to work in Europe, where availability might soon become a real problem. Ammonium Dichromate can't be shipped by air, its a strong carcinogen etc. the whole bit… What about residual dichromate in the carbon print for instance…. if it is a carcinogen it's only a matter of time before it will be branded.
Well first….. am I right in that statement….. how big a problem is this in real life???? I have zero experience at this point.
There is a process floating around called the The Chiba System.
It use Ammonium ferric citrate as the sensitizer and 0.3 % Hydrogen Peroxide as developer. Both largely non toxic especially compared to Ammonium Dichromate.
Is this process for real or just BS….. Would be interesting the hear what the real pros doing carbon printing here has to say about this.
And how does it effect the quality and archival properties of carbon prints?
See
http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&ved=0CDkQFjADOAo&url=http%3A%2F%2Fpolychrome.nl%2Ffile_download%2F3%2F&ei=RdU8U_GGIurRsQTr2oDQDg&usg=AFQjCNH9QxcCD3ot1LG1VzoV7sNKrDZwHw&sig2=d5fKNuwobqsJyV9VG5npig
Pete Watkins
3-Apr-2014, 01:55
i've posted about this before. From September 2017 Ammonium and Potassium Dichromates WILL be banned throughout the EEC by the European Parliment.
These chemicals are allegedly so deadly that we can use them until 2017, which gives a clue as to the mentality of the idiots who are banning them.
I don't believe that they have any idea about the consequencies of this ban. This stuff, in my opinion, is no more deadly than the petrol (gas) that you put into the fuel tanks of your cars.
Potassium Dichromate is not highly flammable but those who govern us still intend to ban it.
If anybody knows of a replacement chemical suitable for use in Gum printing or certain Cyanotype formulas please share your knowledge.
Pete.
Pete,
Check out the link I put in my first post.
It gives supposedly an alternative to Ammonium Dichromate. Which apparently is a strong carcinogen……. I don't know what the facts are.
BUt I am very interested in working with carbon printing and one reason is that carbon print development do not use any chemicals….. only water…… So dichromate problems and regulations is not something I can take lightly, going forward. If I go ahead with carbon printing it's something I'd like to stick with and get good at so I need to know I won't have problems with dichromate issues in my prints. And I am fully aware that dichromate has been used for over 100 years.
It will be interesting if anyone of the skilled carbon print practitioners here will address this issue and the alternative process.
I feel bad about crashing the party like this, but there you have it…..
/gth
i've posted about this before. From September 2017 Ammonium and Potassium Dichromates WILL be banned throughout the EEC by the European Parliment.
These chemicals are allegedly so deadly that we can use them until 2017, which gives a clue as to the mentality of the idiots who are banning them.
I don't believe that they have any idea about the consequencies of this ban. This stuff, in my opinion, is no more deadly than the petrol (gas) that you put into the fuel tanks of your cars.
Potassium Dichromate is not highly flammable but those who govern us still intend to ban it.
If anybody knows of a replacement chemical suitable for use in Gum printing or certain Cyanotype formulas please share your knowledge.
Pete.
desertrat
3-Apr-2014, 08:20
If the dichromates can't be successfully replaced, there is a UK based Ebay vendor selling a set of instructions describing how to make potassium dichromate from readily available chemicals. I'm aware of a 19th century process that uses chrome green pigment (Cr2O3), potassium carbonate, potassium nitrate, a crucible, and a furnace. I think the process for sale on Ebay uses the ingredients in solution at room temperature.
The Chiba System is interesting but not a satisfactory replacement for dichromate in carbon printing IMO.
More promising is a chemical called DSA, 4,4'diazidostilbene, called DSA. Long thread on the subject on APUG, http://www.apug.org/forums/forum42/92732-diazo-sensitized-carbon-transfer.html There are pros and cons associated with a DSA workflow, but for the time being the cons prevail in the balancing act that I make.
My personal opinion is that the use of dichromate in carbon printing does not pose a serious health issue for the worker, assuming reasonable precautions, and that the small amounts that are used are easy to neutralize and dispose of without risk to the environment. In the past carbon printers used wasteful tray sensitizing that resulted in the disposal of a fair amount of dichromate in the environment, but today most serious workers use some form of brush or roller sensitizing that uses a very small amount of very diluted dichromate solutions to sensitize. For example, in my own work flow I use only 30 ml of a 3%-6% solution of dichromate to sensitize with a roller a 20" X 25" sheet of carbon tissue. That amounts to about 0.4 - 0.8 grams of dichromate per print this size, with no waste. If you do the math you will see that even if you print extensively with carbon over the next three decades your total use of dichromate will not amount to more than 4-5 pounds.
Sandy
Huh, so how does one get into the dichromate "importing" business in the EU, someone not me would wonder, toottaly not me.
Nathan Potter
3-Apr-2014, 17:29
Early in my career I used large amounts of Ammonium and Potassium Dichromate to oxidize the surface of molybdenum thin sheets to be used for metal mask manufacture. The handling was careless and the total volume over a few years was tens of pounds. In retrospect that was a very unwise process but hey, I'm 80 now and never have had any discernible side effects from the exposure.
I'm guessing that the EU is more concerned about the possible buildup of Dichromate in the environment but cannot find a solution except to outright ban the material.
Nate Potter, Austin TX.
To address another concern mentioned by the OP, carbon prints would not normally contain any dichromate after processing. During processing some dichromate leeches into the fiber of paper prints but this is normally removed by soaking the print for a few minutes in a solution of sodium or potassium bisulfite/metabisulfite.
Sandy
Thanks Sandy I was just about to ask those specific questions, that is. how much residual dichromate is retained in the print itself. Personally I don't have problem of handling the stuff in the darkroom in a responsible and safe manner. What would be worrisome would be if any PC and chemically obsessive individual or authority could make a claim against the prints, and thus be able to cast aspirations or right out ban public use and sale. The C word is very dangerous.
So what your are saying is that the initial pre-exposure sensitization would load the print with 0.4-08 gram of dichromate. This amount is evenly distributed throughout the gelatine layer? Or on a the surface? The Chromium then hardens the gelatine by a cross binding in the photo chemical reaction, proportional to total illumination received. On development the non hardened gelatine is washed away, presumably with the chromium that has not bound to the gelatine. If not developed the chromium will continue to crossbind to the gelatine even in the absence of light.
So the development bath will contain dichromate, right? Say an average scene has 50 % illumination. Then 0.2-0.4 gram of dichromate would be in the developer (water). If the developer is 1 liter in volume you would have about 300 ppm concentration in the developer. You would have a total of 0.3 gram of dichromate cross bound in the gelatine and thus in the print. The bound dichromate is not toxic? Can it revert to non bound if the print becomes wet for instance?
Sorry to be nerdy about this….. I am definitely not trying to ginn up problems. But carbon printing is too important a process to find ourselves blindsided. Clearly research should continue to find even safer sensitizers.
Chromium compound toxicology……. warning….not nice reading
http://digitalfire.com/4sight/hazards/ceramic_hazard_chromium_compounds_toxicology_330.html
/gth
To address another concern mentioned by the OP, carbon prints would not normally contain any dichromate after processing. During processing some dichromate leeches into the fiber of paper prints but this is normally removed by soaking the print for a few minutes in a solution of sodium or potassium bisulfite/metabisulfite.
Sandy
Chomium(VI) from dichromate is converted into chromium(III) after exposure and only this one will be say with hardened gelatin on the print.
Unexposed chromium(VI) will go to developing batch.
I'm using nitryl gloves for soaking and developing and I don't feel scared by chromium at all.
I remember 20 years ago in school nobody cared too much about dichromates.
Of course it can cause injures to your skin if you leave it there and be dangerous if you breathe dust, but wearing gloves and being sane should keep you safe.
Bad news about banning dichromates, but I've recently found another 1kg jar with PD in my garage so I won't need more in my life ;)
Struan Gray
4-Apr-2014, 05:30
Pete, can you give more detail about the banning of dichromates in carbon printing?
I've had a trawl through the REACH and other EU legislation and can't find anything relevant. The legislation aimed at big industrial users may make dichromates harder to come by, but I don't see anything that will stop the specialist chemical suppliers selling it to carbon printers.
Most of the unreduced dichromate comes out in the mating bath when the exposed and sensitized tissue is mated with the final support. The mating bath can be reused to save water, in fact this is best procedure for carbon printing as old/flat water avoid gases that may be in water fresh from the faucet. My estimate is that about 95% of the unreduced dichromate comes out of the tissue in the mating bath, the rest would come out in warm water development.
The only significant health risk to the carbon printer is inhalation of the dichromate powder when mixing the solutions, and/or ingestion. Both risks are pretty easy to minimize. You also want to wear nitryl gloves to protect your hands from the dilute solution, but here the risk is primaily dermatological as the solutions are so dilute.
Sandy
Andrew O'Neill
4-Apr-2014, 07:55
Great. So now I have to stock up on AD?
Pete Watkins
4-Apr-2014, 09:38
Struan,
I was informed of the oncoming ban by a supplier in London. They let me know the source of their information. It's a part of the UK Health & Safety Executive, a government department. They will be monitering the ban but it is a European directive, pushed out by The EEC. Hopefully it will be reversed if we ever get e vote to leave that organisation.
If you PM me your e-mail address I'll foreward you the e-mail that I recieved from them. If anybody else in EEC countries wants to see it just do the same.
Good news for the rest of the world, unless your government is stupid enough to join the EEC this ban will NOT apply to you.
Pete.
Sandy,
Just finished reading the DSA thread on APUG. Thanks for the link.
In your opinion, if one "started from scratch" in developing ones Carbon printing workflow do you see any intrinsic problems in achieving the same results (image quality, print stability etc) with the DSA methods vs traditional AD methods? And if so, can you comment about what areas you would be apprehensive about.
/gth
The Chiba System is interesting but not a satisfactory replacement for dichromate in carbon printing IMO.
More promising is a chemical called DSA, 4,4'diazidostilbene, called DSA. Long thread on the subject on APUG, http://www.apug.org/forums/forum42/92732-diazo-sensitized-carbon-transfer.html There are pros and cons associated with a DSA workflow, but for the time being the cons prevail in the balancing act that I make.
My personal opinion is that the use of dichromate in carbon printing does not pose a serious health issue for the worker, assuming reasonable precautions, and that the small amounts that are used are easy to neutralize and dispose of without risk to the environment. In the past carbon printers used wasteful tray sensitizing that resulted in the disposal of a fair amount of dichromate in the environment, but today most serious workers use some form of brush or roller sensitizing that uses a very small amount of very diluted dichromate solutions to sensitize. For example, in my own work flow I use only 30 ml of a 3%-6% solution of dichromate to sensitize with a roller a 20" X 25" sheet of carbon tissue. That amounts to about 0.4 - 0.8 grams of dichromate per print this size, with no waste. If you do the math you will see that even if you print extensively with carbon over the next three decades your total use of dichromate will not amount to more than 4-5 pounds.
Sandy
DSA available worldwide
http://www.chemicalbook.com/ChemicalProductProperty_EN_CB9384077.htm
Looks like about $0.60 per 8x10 print?
"In your opinion, if one "started from scratch" in developing ones Carbon printing workflow do you see any intrinsic problems in achieving the same results (image quality, print stability etc) with the DSA methods vs traditional AD methods? And if so, can you comment about what areas you would be apprehensive about."
Since I have not actually established a good work flow with DAS, 4,4'diazidostilbene, I can only speculate. DAS worked very well in the Ultrastable color carbon system but so far as I know it is not currently being used by any of the top monochrome carbon printers. Areas that would concern me are, 1) the low saturation point of DAS, about 3% as I believe, in comparison to about 10% for potassium dichromate, and 30% for ammonium dichromate, 2) the heavy stain that DAS gives to images on paper, making it necessary to use the very powerful oxidizer potassium permaganate as a clearing agent, 3) the reduced sensibility, about a stop from what I have read, compared to dichromate, 4) the light sensitivity and keeping qualities of DAS.
Sandy
DSA available worldwide
http://www.chemicalbook.com/ChemicalProductProperty_EN_CB9384077.htm
Looks like about $0.60 per 8x10 print?
Sorry, just to point out that I mistakenly called 4,4'diazidostilbene "DSA" in a previous message. That should have been "DAS."
Sandy
As one who is just starting down the Carbon Printing road (and so taken with it I am converting my darkroom to solely Carbon Printing and selling off my four enlargers) I have been buying up stocks of Ammonium Dichromate as they become available (in the UK), I currently have 500 grams of crystals and am hoping to add to that before the EU ban comes fully into place (I say fully as a large number of companies will only sell Ammonium Dichromate to large commercial users or Educational establishments.
On another note, I was printing some tissues on Thursday and I took my gloves off between the sensitising and exposing stages, when I completed the exposure I mated the exposed tissue to the final medium forgetting to put the gloves back on. What made this worse was earlier in the day I managed to cut my finger on one of my mitre trimming knives (whilst making a frame) and although I had a waterproof plaster on I am pretty sure some of the Dichromate laden liquid would have got in. Nothing I can do about it now but a lesson learned.
One Exposure is not going to to do you in. It's cronic exposure over time that makes a difference, at least for small doses per exposure. But it's fairly nasty stuff. It does not matter if your have wound or not…. Ammonium dichromate goes straight through your intact skin. You need to protect your skin at all times. Check out...
http://digitalfire.com/4sight/hazards/ceramic_hazard_chromium_compounds_toxicology_330.html
At the bottom of the page they recommend some skin ointments that will keep the dichromate out that you can wear on your hands ( I guess you can wear that inside your gloves), or Zink Oxide ointment in your nose is also good. It IS a carcinogen and it will even mess with your DNA. But it is is chemical and to really affect you health, you have to be subjected to sustained exposure - that's how I read it. But you see some YouTube videos where folks are handling this stuff with bare hands…. not good.
I think you are probably in more danger from being "exposed" having 1 kg of a known strong carcinogen in your house….. that **could** weak havoc with your life in todays world.
And that's where I am coming from …… carbon printing is otherwise squeaky clean…. carbon pigment, gelatine and water + just about the most fabulous printing method there is… if only we could get rid of the dichromate…..
As one who is just starting down the Carbon Printing road (and so taken with it I am converting my darkroom to solely Carbon Printing and selling off my four enlargers) I have been buying up stocks of Ammonium Dichromate as they become available (in the UK), I currently have 500 grams of crystals and am hoping to add to that before the EU ban comes fully into place (I say fully as a large number of companies will only sell Ammonium Dichromate to large commercial users or Educational establishments.
On another note, I was printing some tissues on Thursday and I took my gloves off between the sensitising and exposing stages, when I completed the exposure I mated the exposed tissue to the final medium forgetting to put the gloves back on. What made this worse was earlier in the day I managed to cut my finger on one of my mitre trimming knives (whilst making a frame) and although I had a waterproof plaster on I am pretty sure some of the Dichromate laden liquid would have got in. Nothing I can do about it now but a lesson learned.
Jim Fitzgerald
5-Apr-2014, 19:13
As one who is just starting down the Carbon Printing road (and so taken with it I am converting my darkroom to solely Carbon Printing and selling off my four enlargers) I have been buying up stocks of Ammonium Dichromate as they become available (in the UK), I currently have 500 grams of crystals and am hoping to add to that before the EU ban comes fully into place (I say fully as a large number of companies will only sell Ammonium Dichromate to large commercial users or Educational establishments.
On another note, I was printing some tissues on Thursday and I took my gloves off between the sensitising and exposing stages, when I completed the exposure I mated the exposed tissue to the final medium forgetting to put the gloves back on. What made this worse was earlier in the day I managed to cut my finger on one of my mitre trimming knives (whilst making a frame) and although I had a waterproof plaster on I am pretty sure some of the Dichromate laden liquid would have got in. Nothing I can do about it now but a lesson learned.
I'm glad that I live on this side of the pond. I have several pounds of both dichromates and as a dedicated carbon printer I know I have enough. I just hope they do not ban it here. If so, I'll buy more right away. None of the other printing processes gives me what I see and feel.
Ed, glove are a must. We all get careless once in a while ... me too.
Struan Gray
6-Apr-2014, 02:33
Struan,
I was informed of the oncoming ban by a supplier in London. They let me know the source of their information. It's a part of the UK Health & Safety Executive, a government department. They will be monitering the ban but it is a European directive, pushed out by The EEC. Hopefully it will be reversed if we ever get e vote to leave that organisation.
If you PM me your e-mail address I'll foreward you the e-mail that I recieved from them. If anybody else in EEC countries wants to see it just do the same.
Good news for the rest of the world, unless your government is stupid enough to join the EEC this ban will NOT apply to you.
Pete.
Thanks Pete. This wouldn't be the first time HM Govt. has over-enthusiastically applied EU safety law. The EU directives I have seen say nothing whatsoever about use of the raw chemical by private carbon printers, and even a commercial carbon printer would be exempt as the amounts of hexavalent chromium in the final product are so vanishingly small. The problem, if any, will be one of over-cautious suppliers not wanting to ship it to unaccredited buyers.
The suppliers of laboratory chemicals I would order from here don't have any plans to discontinue standard dichromates in hobby scale amounts. But then, in the past, I have always ordered such things as a member of university research department - things are often more difficult for a private individual.
I am paranoid enough about safety that I don't want dichromates in the house with my kids. Not without building a lockable darkroom with a proper fume cupboard at any rate. But colour carbon prints are something I long to try, once time and space are available.
Struan
Peter De Smidt
6-Apr-2014, 08:48
How should one work with the powder safely? I suppose I could move the powder to the de-tached garage and mix the solutions outside with a cartridge respirator on. That won't make the neighbors wonder.
I've had a trawl through the REACH and other EU legislation and can't find anything relevant. The legislation aimed at big industrial users may make dichromates harder to come by, but I don't see anything that will stop the specialist chemical suppliers selling it to carbon printers.
See Commission Regulation No. 348/2013. To use dichromates after September 2017, you need to have applied for authorisation, and the last date for application is in March 2016.
Can you buy it and ship it in Sweden?
BH photo will sell it but only at their store in NYC…. no shipping. (ETC.)
I think we all end up at the same place… "I can handle it safely…. BUT"……
Carbon and other processes that use dichromates are too important to end up as a historical "but.."
So let's put out pants on and develop safe work flow that assures the continuation of carbon printing et. al.
Some already have:
http://carbonprinting.wordpress.com/category/process/
Thanks Pete. This wouldn't be the first time HM Govt. has over-enthusiastically applied EU safety law. The EU directives I have seen say nothing whatsoever about use of the raw chemical by private carbon printers, and even a commercial carbon printer would be exempt as the amounts of hexavalent chromium in the final product are so vanishingly small. The problem, if any, will be one of over-cautious suppliers not wanting to ship it to unaccredited buyers.
The suppliers of laboratory chemicals I would order from here don't have any plans to discontinue standard dichromates in hobby scale amounts. But then, in the past, I have always ordered such things as a member of university research department - things are often more difficult for a private individual.
I am paranoid enough about safety that I don't want dichromates in the house with my kids. Not without building a lockable darkroom with a proper fume cupboard at any rate. But colour carbon prints are something I long to try, once time and space are available.
Struan
Struan Gray
7-Apr-2014, 02:19
See Commission Regulation No. 348/2013. To use dichromates after September 2017, you need to have applied for authorisation, and the last date for application is in March 2016.
I have read that, and the original REACH legislation to which it refers. The authorisation process is for companies selling goods to the general public which include hexavalent chromium in the final product (above a certain threshold value). It does not apply to industrial processes which use hexavalent chromium to produce a final product which contains only trace amounts (like a carbon print). It also does not apply to some of the biggest industrial excreters of hexavalent chromium into the environment - such as some steel and aerospace manufacturers - because they are specifically exempted, but that's a political argument for another day.
The ban is not on use, it is on sales to the general public. The distinction may seem minor, but it really isn't.
Struan Gray
7-Apr-2014, 02:29
Can you buy it and ship it in Sweden?
Yes. Not as a private individual, but as a single-person company (costs a few tens of dollars and a week to set up), or a school teacher, or someone working at pretty well any company whatsoever, I can order it and it will be shipped to me.
The real key is to have an organisation number, which in the EU is usually the same as your VAT number. They are not hard to obtain, if you are serious about what you do.
Note that I have a twenty year career as a research scientist behind me, and in that career I used all manner of substances and procedures which would be truly dangerous in the wrong hands. I have been responsible for chemical and other safety for a whole university science department. Which is not to brag, but to show that I know how to talk to chemical suppliers, and how comply with safety regulations. (And, FWIW, how to assess procedures and materials for compatibility with a happy and stable home life).
I have followed the DAS story on APUG with great interest. I'm not that keen on a molecule with two benzene rings and a bunch of nitrogen groups either, but it's better than hexavalent chromium, both for me and for the environment. Easier to dispose of too. My personal dream is colour Woodburytype, or Woodburytype over inkjet, which eliminates the exposure and development stages altogether. Thus far though, it's all in the mind.
How should one work with the powder safely? I suppose I could move the powder to the de-tached garage and mix the solutions outside with a cartridge respirator on. That won't make the neighbors wonder.
Peter,
It is very easy to handle and use dichromate safely. Basically, do this.
Avoid contact with eyes, skin, & clothing.
Avoid Breathing dust. Use with adequate ventilation.
Protect your hands with gloves and after handling dichromate.
Once the powder is in the dilute solutions (3%-8%) needed for carbon printing we are using it in such small quantities that the risk factor is extremely small.
Sandy
I would like to make it clear that I was somewhat apprehensive about starting this thread, should it in any way cast the tremendous work and effort by Sandy and others in a bad light.
Obviously I have not added anything that was not already known.
I have nothing but admiration for the creative work put in by many people to revitalize and make carbon printing accessible and documented to be able to live on. It's easy to speak of alternates when you haven't spent years developing a work flow that works consistently with outstanding results.
Clearly dichromates CAN be handled safely by responsible practitioners.
What worries me is the regulatory environment and general attitude towards chemistry and science from regulators, politician and an uninformed public.
Perhaps I am paranoid but it is not all that hard to come up with scenarios with bad outcomes for carbon printing in todays world, considering what is known about hexavalent chromium compounds.
If "we" can stop that (remote?) possibility cold it's worthwhile.
The object is to ensure that carbon printing and prints will exist for another 100 years.
What other compounds could possibly be used to photochemically harden gelatine?
Can we step back and look at the basic process needed and find solutions?
Maybe these questions belong on APUG.
/gth
Pete Watkins
7-Apr-2014, 10:55
gth,
Well said. I have no idea what will happen in EEC countries but I fear the worst. We are ruled by un-elected morons.
Good luck to the rest of the world.
Pete.
Struan Gray
7-Apr-2014, 11:51
I too would like to make it clear that I in no way think that other people should not be using dichromates in their private photographic work, or that I think it is unsafe to do so.
One thing that has changed in the time since I started working in labs is the definition of 'adequate ventilation'. A fume hood or well-designed darkroom ventilation would make a lot of sense, rather than trusting to luck. Similarly, I would wear safety goggles to guard against accidental splashes or dust entering my eyes.
Sandy: do you use a reducer to convert the chromium VI before disposal? I have seen suggestions to use sodium thiosulphate - do you have any other recommendations?
DAS is a satisfactory way of making carbon prints, if you are uncomfortable with dichromates use an alternative and get on with it, dont look back. Look at Todd Ganglers wonderful colour work, there is nothing to fear, all it takes is some new work habits. Hard if you have an established workflow but if you are just starting its a good way to go.
Erik Larsen
7-Apr-2014, 13:20
[QUOTE
Sandy: do you use a reducer to convert the chromium VI before disposal? I have seen suggestions to use sodium thiosulphate - do you have any other recommendations?[/QUOTE]
Sodium sulfite works as well.
One nice thing about ammonium or pottasium dichromate (if there can be a nice thing) is that the stuff I have purchased in pound quantities is granular, not powdery fluff so there is no dust created when weighing out and mixing. That being said please use common sense, wear gloves etc when handling. The amounts we use is minuscule per print and it's hazards are sometimes blown out of proportion.
"I would like to make it clear that I was somewhat apprehensive about starting this thread, should it in any way cast the tremendous work and effort by Sandy and others in a bad light."
No problem on my part with the discussion. And the issue is one of interest no only to carbon printers, but also to all of the other photographic processes that are based wholly or in part on dichromate, including gum bichromate and most of the alternative printing processes.
At this time the only alternative I see to dichromate is DAS and there are pros and cons with the work flow of each. If the question is what will be available in the future, who knows? Right now, in my place and time, DAS is both more expensive and less readily available than dichromate.
Sandy
"Sandy: do you use a reducer to convert the chromium VI before disposal? I have seen suggestions to use sodium thiosulphate - do you have any other recommendations?"
In my work flow most of the unreduced hexavalent chromium is removed from the sensitized and exposed tissue in the mating bath, where the tissue is combined with the final support. This bath is reused, not discarded. The sandwich is squeegeed over a paper support that picks up excess solution. The paper support is discarded as solid waste. The only thing that goes down the drain, to a septic tank, is the developing water, which would contain a very small amount of chromium VI. My understanding is that in the pH of the septic tank the Cr(VI) will eventually be reduced to Cr(III) by organic matter.
Sandy
Struan Gray
7-Apr-2014, 23:39
Thanks Sandy, good info.
sanking
11-Apr-2014, 11:05
The object is to ensure that carbon printing and prints will exist for another 100 years.
What other compounds could possibly be used to photochemically harden gelatine?
Can we step back and look at the basic process needed and find solutions?
Maybe these questions belong on APUG.
/gth
I started a thread on the yahoo carbon forum about DAS to have a conversation about non-dichromate alternatives for carbon printing.
I am not optimistic about DAS itself. Although this is a chemical known to work, with certain work-flow issues, it is not easy to purchase, and is quite expensive even in bulk orders. Try $500 a kilo in bulk orders ot 10 kilos or more from China. That would make it difficult for even suppliers like Bostick & Sullivan and Photographer's Formulary to buy and sell the stuff at a reasonable price to hobbyists. It seems that the main industrial use of DAS no longer exists, thus the reason for the very high price since it has to be produced for a specific purpose without broad general application.
On the other hand there are some other potential sensitizing alternatives from the world of silk screening that may have properties that work for carbon printing. If any of the skilled carbo printers on the Yahoo forum get interested in the subject at least we will have somebody to test the chemicals who actually knows how to make a good carbon print.
Sandy
The TCIi price for DAS is about $90 per 25 g. There is a some mention of 2mg of DAS per sq in of tissue on APUG. That translates to $0.60 per 8x10 print.
The 25 gram price is advertised on the TCI site, but I have no idea if the emulsion concentration is valid. Assume it's twice that of the APUG data and that you have 20 % loss in handling and your are at $1.45 per 8x10. If one out of ten prints makes it through the workflow it is $15 per good print and might still be justified considering other costs to produce that print.
Assuring long term availability might be a nastier question.
What about the
Ed Bray
13-Apr-2014, 00:39
If anyone needs Ammonium Dichromate in the UK, there is some available on ebay at the moment. I bought 5kgs yesterday.
Further required DAS concentration and cost.
David Chalmers at
http://carbonprinting.wordpress.com/category/process/
Says he uses 0.5% DAS sensitizer in the emulsion.
If I use an emulsion of 1/16 " x 8" x10 " I use up 5 cubic inch of carbon emulsion. Counting only weight of gelatine that is 104 gram (gelatine relative density of 1.3).
Does that sound reasonable?
At 0.5% DAS we get 0.5 gram of DAS per 8x10 print.
THat is $1.8 in DAS cost for a 8x10 print using the commercial price of $90 per 25 gram or three times my previous calculation. Which would start to hurt if one considers losses to get to a final print.
Chalmers' concentration was high so the cost might be in the $1 per 8x10 which is comparable to other costs in the process although much higher than the cost of dichromate.
That may be a necessary cost of business for a more "safe" process.
That yahoo group seems like the place for this……. But how the hell do you read that thing…??? I feel stupid ….. you have to look at each message individually….. there is even a button for "source" who needs that????…. and if you click "see all messages" it opens up one or two and you have to make another click….Is there a way to make the display like LFF or APUG? Sorry to be off topic but if someone is used to that mess tell me how I make it readable….. I need a "Yahoo for Dummies"…...It's like some bulletin board in 1987….
I started a thread on the yahoo carbon forum about DAS to have a conversation about non-dichromate alternatives for carbon printing.
I am not optimistic about DAS itself. Although this is a chemical known to work, with certain work-flow issues, it is not easy to purchase, and is quite expensive even in bulk orders. Try $500 a kilo in bulk orders ot 10 kilos or more from China. That would make it difficult for even suppliers like Bostick & Sullivan and Photographer's Formulary to buy and sell the stuff at a reasonable price to hobbyists. It seems that the main industrial use of DAS no longer exists, thus the reason for the very high price since it has to be produced for a specific purpose without broad general application.
On the other hand there are some other potential sensitizing alternatives from the world of silk screening that may have properties that work for carbon printing. If any of the skilled carbo printers on the Yahoo forum get interested in the subject at least we will have somebody to test the chemicals who actually knows how to make a good carbon print.
Sandy
sanking
13-Apr-2014, 12:57
That yahoo group seems like the place for this……. But how the hell do you read that thing…??? I feel stupid ….. you have to look at each message individually….. there is even a button for "source" who needs that????…. and if you click "see all messages" it opens up one or two and you have to make another click….Is there a way to make the display like LFF or APUG? Sorry to be off topic but if someone is used to that mess tell me how I make it readable….. I need a "Yahoo for Dummies"…...It's like some bulletin board in 1987….
The face of the current situation at Yahoo is Marissa Mayer.
The forums were much easier to follow before the current series of changes made under Mayer, which still seem to be in flux. On the other hand, the galleries are much improved so your work there can look very good if is submitted in appropriate form.
Sandy
sanking
17-Apr-2014, 14:42
How strong a DAS sensitizer you would need depends on several factors other than the sensitizer itself (pigment loading, pigment type, gelatin type, tissue thickness, etc.) , but it should not be all that hard to figure out for someone with experience in carbon printing with dichromate.
There may be less expensive alternatives in the Diazido type sensitizers produced for screen printing. Someone sent me one of these sensitizers to test and on the second iteration I managed to make a pre-sensitized carbon tissue with a good tonal scale, high Dmax, and good printing speed. I lapped the Stouffer step wedge with Pictorico in the center to show the effect of the extra density over the Stouffer step wedge. Exposure was made in direct sun, for four minutes. The Dmax is about log 2.05, as high as good silver papers. The attached file is a direct scan of the carbon step wedge, with no post-scan adjustments to the histogram.
What I don't know is the keeping quality of this tissue compared to tissue sensitized with DAS, which is of course very stable. I have not cleared the step wedge yet either, but without clearing it has a lot less stain than one would see with DAS. But in terms of image quality alone this screen sensitizer gives results that appear to be as good in terms of Dmax and tonal range as dichromate sensitized tissue.
Sandy
Further required DAS concentration and cost.
David Chalmers at
http://carbonprinting.wordpress.com/category/process/
Says he uses 0.5% DAS sensitizer in the emulsion.
If I use an emulsion of 1/16 " x 8" x10 " I use up 5 cubic inch of carbon emulsion. Counting only weight of gelatine that is 104 gram (gelatine relative density of 1.3).
Does that sound reasonable?
At 0.5% DAS we get 0.5 gram of DAS per 8x10 print.
THat is $1.8 in DAS cost for a 8x10 print using the commercial price of $90 per 25 gram or three times my previous calculation. Which would start to hurt if one considers losses to get to a final print.
Chalmers' concentration was high so the cost might be in the $1 per 8x10 which is comparable to other costs in the process although much higher than the cost of dichromate.
That may be a necessary cost of business for a more "safe" process.
Drew Wiley
17-Apr-2014, 15:44
What has to be kept in mind is not just hypothetical dangers to a limited group of end-users, such as carbon printers, but the overall effect of a chemical category
both during manufacture and in cumulative disposal, especially waterways. And there's no guarantee the EPA won't adopt some EU proscription here, once a compound is on the radar. And frankly, the anecdotes of a few artists aren't going to have a lot of weight on the medical evidence itself. What there does need to
be is some kind of small volume exclusion specifically for artistic use, much like the continuation of limited amounts of cadmium or lead pigments in artist's oil paints. But you just never know - there's the other giant gorilla on the block that has to be kept in rein, and some of these chromium compounds have already entered the realm of drug abuse. I't almost unbelievable that humans would deliberately get this stuff in their systems, but they do; and consequently there is monitoring from that angle too. Hexavalent chromium is a very very bad term right now in the public perception, and this might be equivalent to someone raising
Cain about the luminous hands of a Mickey Mouse watch after a nuclear bomb test, but that's unfortunately the way the world works. Good luck.
How strong a DAS sensitizer you would need depends on several factors other than the sensitizer itself (pigment loading, pigment type, gelatin type, tissue thickness, etc.) , but it should not be all that hard to figure out for someone with experience in carbon printing with dichromate.
There may be less expensive alternatives in the Diazido type sensitizers produced for screen printing. Someone sent me one of these sensitizers to test and on the second iteration I managed to make a pre-sensitized carbon tissue with a good tonal scale, high Dmax, and good printing speed. I lapped the Stouffer step wedge with Pictorico in the center to show the effect of the extra density over the Stouffer step wedge. Exposure was made in direct sun, for four minutes. The Dmax is about log 2.05, as high as good silver papers. The attached file is a direct scan of the carbon step wedge, with no post-scan adjustments to the histogram.
What I don't know is the keeping quality of this tissue compared to tissue sensitized with DAS, which is of course very stable. I have not cleared the step wedge yet either, but without clearing it has a lot less stain than one would see with DAS. But in terms of image quality alone this screen sensitizer gives results that appear to be as good in terms of Dmax and tonal range as dichromate sensitized tissue.
Sandy
That is terrific Sandy…… Few if any are as qualified to take on this issue as you are. Thanks!
Erik Larsen
17-Apr-2014, 18:24
That's encouraging Sandy. Is this mystery sensitizer as economical as the dichromates? Does it respond the same way regarding contrast control? Off topic a little, might it work with gum printing as well?
sanking
17-Apr-2014, 19:00
That's encouraging Sandy. Is this mystery sensitizer as economical as the dichromates? Does it respond the same way regarding contrast control? Off topic a little, might it work with gum printing as well?
It probably won't be as economical for me as dichromate. When I began working with alternative processes back in the early 1980s I bought 20 lbs of dichromate for $19.95. I still have more than half of that on hand so dichromate costs me almost nothing. However, my understanding is that the cost per kilo of the "mystery" sensitizer should be about $100-145, and is readily available as it it widely used in the screen printing industry.
I am not sure if this sensitizer works for gum or not. However, there is a current thread on the carbon forum on DAS where someone mentions another screen sensitizer that he has been using for gum and for carbon experiments. He did not mention the CAS number but I don't believe it is the same one I am using.
And the sensitizer does respond to contrast control as dichromates, though the range appears to be a bit more limited so higher pigment loading seems necessary. The most important thing I don't know is how stable the pre-sensitized tissue will be, and that will take some months to determine. The other issue is that I have not figured out how to brush it on as the solution seems to stay on the surface rather then penetrate all the way through the tissue as happens when we brush sensitize dichromate.
Sandy
Erik Larsen
17-Apr-2014, 19:36
It probably won't be as economical for me as dichromate. When I began working with alternative processes back in the early 1980s I bought 20 lbs of dichromate for $19.95. I still have more than half of that on hand so dichromate costs me almost nothing. However, my understanding is that the cost per kilo of the "mystery" sensitizer should be about $100-145, and is readily available as it it widely used in the screen printing industry.
I am not sure if this sensitizer works for gum or not. However, there is a current thread on the carbon forum on DAS where someone mentions another screen sensitizer that he has been using for gum and for carbon experiments. He did not mention the CAS number but I don't believe it is the same one I am using.
And the sensitizer does respond to contrast control as dichromates, though the range appears to be a bit more limited so higher pigment loading seems necessary.
Sandy
Thanks Sandy, that price seems reasonable. Like you, I have pounds of both amm. And k dichromate, but it looks like our fellow printers in other parts of the world might have a hard time obtaining it in the future. I don't know if I would like to learn another workflow with this screen printing sensitizer for carbon, not to mention carbro but it does interest me for gum printing where I use a lot more dichromate than in carbon. It might be a good hedge against the future to have an alternative to dichromates if our govt. decides I'm too irresponsible to handle them and bans their use:) I appreciate the info.
Erik
sanking
17-Apr-2014, 19:51
That is terrific Sandy…… Few if any are as qualified to take on this issue as you are. Thanks!
It is an interesting challenge, and I am glad to have someone interested who can talk to the chemists.
If it works out I may go back to color carbon printing??? I did that at one time with analog separation negatives, shot in the camera through 25, 58 and 47 filters. Making color carbon prints with digital separations almost sounds like cheating compared to that work flow!!
Sandy
A couple of stupid questions Sandy..
When you tested the emulsion with the step wedge…. this is a step edge transparency that you contact printed onto the emulsion sample. Then you developed that and took a picture of the wedge print with a digital camera. What are the steps in the wedge… 1 stop per step?
Can you develop in warm water, or do you have to use other chemicals?
Why would you want to brush on the sensitizer rather than mix it in the emulsion. To avoid marginal emulsion stability when sensitized?
Or set contrast grade at print time?
sanking
19-Apr-2014, 07:06
"When you tested the emulsion with the step wedge…. this is a step edge transparency that you contact printed onto the emulsion sample. Then you developed that and took a picture of the wedge print with a digital camera. What are the steps in the wedge… 1 stop per step? "
In this case I scanned the step wedge since it is small enough to do so, and being on smooth Yupo texture is not a problem as it can be with some papers. Each of the step wedges is log 0.15 density, or the equivalent of 1/2 stop. A full stop in sensitometry is log 0.3.
"Can you develop in warm water, or do you have to use other chemicals?"
Development is in warm water, same as with tissue sensitized in dichromate.
"Why would you want to brush on the sensitizer rather than mix it in the emulsion. To avoid marginal emulsion stability when sensitized? Or set contrast grade at print time?"
In monochrome printing I like to set the contrast grade at the time of printing, to be able to fine-tune it for a specific negative. This is the equivalent of being able to work with a variable contrast paper in silver printing, where you can fine tune contrast with filters. With pre-sensitized tissue you are stuck with the contrast that is built in.
With color my thought process on this would be different as you would want to start with tissue with known and consistent characteristics.
Sandy
"When you tested the emulsion with the step wedge…. this is a step edge transparency that you contact printed onto the emulsion sample. Then you developed that and took a picture of the wedge print with a digital camera. What are the steps in the wedge… 1 stop per step? "
In this case I scanned the step wedge since it is small enough to do so, and being on smooth Yupo texture is not a problem as it can be with some papers. Each of the step wedges is log 0.15 density, or the equivalent of 1/2 stop. A full stop in sensitometry is log 0.3.
"Can you develop in warm water, or do you have to use other chemicals?"
Development is in warm water, same as with tissue sensitized in dichromate.
"Why would you want to brush on the sensitizer rather than mix it in the emulsion. To avoid marginal emulsion stability when sensitized? Or set contrast grade at print time?"
In monochrome printing I like to set the contrast grade at the time of printing, to be able to fine-tune it for a specific negative. This is the equivalent of being able to work with a variable contrast paper in silver printing, where you can fine tune contrast with filters. With pre-sensitized tissue you are stuck with the contrast that is built in.
With color my though process on this would be different as you would want to start with tissue with known and consistent characteristics.
Sandy
Ok, I understand.
Would it be possible to make pre-sensitized tissue in certain fixed contrast grades and then tune it with an additional brush coat at print time.?
That would depend on if you can get ANY sensitizer into the emulsion with brush application.
sanking
19-Apr-2014, 08:47
Ok, I understand.
Would it be possible to make pre-sensitized tissue in certain fixed contrast grades and then tune it with an additional brush coat at print time.?
That would depend on if you can get ANY sensitizer into the emulsion with brush application.
The answer is I don't really know how well this would work. You can brush the sensitizer on the tissue but as I may have mentioned, it does not seem to penetrate very deep into the layer of gelatin. There may be a solution to this by addition of some penetrating agent, but for now I am clueless.
The mechanism of how dichromate penetrates the gelatin layer is not widely understood for that matter. Some people have claimed that you must tray sensitize to get the dichromate to the bottom of the tissue layer, but that is clearly not the case.
Sandy
Sandy, do you know if the Speedball Diazo Sensitizer has been determined NOT to work with gelatine?
In the big thread on this matter at APUG seems they started with the Speedball because it is readily available. But the conclusion is not completely clear that the Speedball stuff will not work. I think it was determined NOT to work, but it was also a matter if too much sensitizer was used in the first experiment.
/gth
sanking
17-May-2014, 20:13
Sandy, do you know if the Speedball Diazo Sensitizer has been determined NOT to work with gelatine?
In the big thread on this matter at APUG seems they started with the Speedball because it is readily available. But the conclusion is not completely clear that the Speedball stuff will not work. I think it was determined NOT to work, but it was also a matter if too much sensitizer was used in the first experiment.
/gth
I gathered that Speedball is capable of producing an image, but how well it does that in comparison to dichromate is not apparent from the thread.
It seems that once Charles Berger noted that the sensitizer used in the Ultrastable was 4,4 ' - diazidostilbene -2,2' - disulfonic Acid Disodium Salt Tetrahydrate (now known as DAS) the conversation shifted to it.
Sandy
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