Ammonium Dichromate replacement for Carbon printing

[gth]

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]

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]

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]

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.

[gth]

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]

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]

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]

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]

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

[gth]

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?