Platinum prints from digital negatives

[sanking]

Bob,

Gum is a great process for some people. I tried it myself many years ago, but eventually came to the conclusion that my vision is more photographic than painterly, and hand crafted processes like carbon and platinum work much better for me.

A good profile should help you to get to where the first print in process is good enough about 50% of the time, but in my work the perfect print nearly always needs two or three iterations by minor adjustments by contrast controls with the process. In carbon we have this both in making the print, and even after the print as it is possible to bring down density by soaking the print in very hot water for up to about a week after it is made. This post processsing density adjustment does not exist with pt/pd.

The key for me in making a great digital negative is the use of a RIP that allows control in terms of ink and percentage of ink deposited at every pixel point on the negative. QTR allows this, the Epson, HP and Canon drivers do not. I would suspect that there is a program somewhere that would give you this control with the Lambda.

BTW, I am tying to get set up to make some three color carbons for the first time in a couple of decades. With the ability to make digital separations and pin registration I am sure this will be much easier than in the past. I replaced the Stoesser punch and registration table you have with a similar one purchased from a company in British Columbia. Man, the Canadian dollar is so low it sure gives the buyer with a US dollar a big break in price.

Sandy

[bob carnie]

Gum is a great process for some people. I tried it myself many years ago, but eventually came to the conclusion that my vision is more photographic than painterly, and hand crafted processes like carbon and platinum work much better for me


Sandy

This is a great way to sum up Gum because my prints really look less like photographs with layers of gum. I am doing one hit gum over palladiums that look more photographic. But once you start putting three layers of gum well the image does transition to a different look.
Are you going to use the transfer of three colours to the paper like Bentley, I imagine there is no other way?? I have found that with four soakings of paper on aluminum the paper sometimes finally lifts off the support which is a pain in the ass.

my punch is working quite nice, btw use it every week.

Bob

[Michael Mutmansky]

HCl = Hydrochloric acid chemical formula

I think that the discussion above is using HCA as a reference to hypo clearing agent, but I've seen some people use HCA to mean Hydro Chloric Acid, so I wanted to be clear that people should not be using that stuff without proper attention to their health. It's volatile, so it gets in your lungs and eyes. It corrodes pretty much all metals, including stainless, so your plumbing will suffer, and while it does work for clearing, it is easy to overdo it and start bleaching if you aren't careful.

While it won't kill you like mercuric chloride, it is really too much risk for people to use without getting suited up, and who wants to do that in a darkroom.


---M

[Vaughn]

Question that has come up elsewhere...

What is the vapor pressure of Potassium oxalate? All I get in my searches is "not available". Does any Potassium oxalate actually rise up into the air from a hot bath of it? Or it is just water vapor?

[Michael Mutmansky]

Question that has come up elsewhere...

What is the vapor pressure of Potassium oxalate? All I get in my searches is "not available". Does any Potassium oxalate actually rise up into the air from a hot bath of it? Or it is just water vapor?

Not sure, but I believe some does get out. It has a slight odor.

Actually, that's not really clear either, since most PO is re-used, so you really have a witches' brew of FO, PO, metal salts, paper size, and who knows what else. I keep mine covered until the pour, and then back under cover after the print is out of it.

---Michael

[Fr. Mark]

Not having the right references in front of me to be sure of vapor pressure, but Potassium Oxalate is a salt of Oxalic acid, as with most salts its vapor pressure will be very low. Smell could be impurities or depending on what else is in the solution, the free acid. Oxalates have some toxicity, but I don't think it is as bad as cyanide. IIRC oxalic acid is the toxic agent in Rhubarb leaves (not stalks, the part I love for pie). People don't usually measure the vapor pressure of salts of organic acids. The value will be a really high number if the material doesn't decompose upon heating before liquifying let alone boiling. Oxalates will probably give off CO2 and CO (carbon dioxide, more/less harmless, and carbon monoxide, very toxic) upon degradation, but again, I no longer have the reference books at my finger tips.

HCl (hydrochloric acid, muriatic acid) is pretty corrosive even in low concentrations and concentrated solutions give off fumes that will sting the eyes and nose/throat if not outright burn them. I was reminded of this when adding acid to water (always do it that way not the other way around!) last night to make cyanotypes. I miss having a fume hood to do chemistry in. that said, I do not ban HCl from my basement. It's a very useful chemical. I'd suggest handling concentrated solutions with good ventilation, splash protection for the eyes and rubber (nitrile) gloves, but that pretty much applies to anything we use for photo chemistry and might not be a bad idea for some kinds of cooking of food! BTW conc HCl is 30-37% so when you have a 5% solution, it's still pretty strong even though 5% doesn't sound like much. True, it will eat stainless (it's stain less not totally impervious unlike the german Rostefrei (rust free---hah!)). But if you dilute it enough, it won't harm your pipes, particularly if you have PVC drain pipes which are pretty much impervious to dilute HCl. Stomach acid is a few percent, maybe even 10% HCl, as anyone with acid reflux will tell you, you want to keep that acid where the body is protected from it (the stomach, not the esophagus) but it isn't immediately dangerous to life with proper handling. Don't bathe in it, but don't overly fear it either. If I've used a lot of HCl, and I have iron and copper drain pipes, I will neutralize it with baking soda first to double "bomb proof" the dilution thing. This makes a lot of fizz (carbon dioxide) so use an over-sized container.

[Fr. Mark]

Sandy, is there someplace I can see the 3 color carbon prints? Also, why not 4 color separations? If you are going to climb that mountain, what's another layer to keep in registration etc etc (hahah)?

[sanking]

Sandy, is there someplace I can see the 3 color carbon prints? Also, why not 4 color separations? If you are going to climb that mountain, what's another layer to keep in registration etc etc (hahah)?

To be clear, I have not made any three-color carbon prints in a long time. At this point I am just trying to get set up to do it, which includes among other thing developing a three-color tissue set.

4-color separations are not needed to get blacks with high Dmax values in carbon as they may be for some graphic art processes.

Sandy

[bob carnie]

I look forward to seeing some of your progress, not for the feint of heart. but when they come out tri Gums they are wonderful I am sure your prints will sing.

To be clear, I have not made any three-color carbon prints in a long time. At this point I am just trying to get set up to do it, which includes among other thing developing a three-color tissue set.

4-color separations are not needed to get blacks with high Dmax values in carbon as they may be for some graphic art processes.

Sandy

[Michael Mutmansky]

Not having the right references in front of me to be sure of vapor pressure, but Potassium Oxalate is a salt of Oxalic acid, as with most salts its vapor pressure will be very low. Smell could be impurities or depending on what else is in the solution, the free acid. Oxalates have some toxicity, but I don't think it is as bad as cyanide. IIRC oxalic acid is the toxic agent in Rhubarb leaves (not stalks, the part I love for pie). People don't usually measure the vapor pressure of salts of organic acids. The value will be a really high number if the material doesn't decompose upon heating before liquifying let alone boiling. Oxalates will probably give off CO2 and CO (carbon dioxide, more/less harmless, and carbon monoxide, very toxic) upon degradation, but again, I no longer have the reference books at my finger tips.

HCl (hydrochloric acid, muriatic acid) is pretty corrosive even in low concentrations and concentrated solutions give off fumes that will sting the eyes and nose/throat if not outright burn them. I was reminded of this when adding acid to water (always do it that way not the other way around!) last night to make cyanotypes. I miss having a fume hood to do chemistry in. that said, I do not ban HCl from my basement. It's a very useful chemical. I'd suggest handling concentrated solutions with good ventilation, splash protection for the eyes and rubber (nitrile) gloves, but that pretty much applies to anything we use for photo chemistry and might not be a bad idea for some kinds of cooking of food! BTW conc HCl is 30-37% so when you have a 5% solution, it's still pretty strong even though 5% doesn't sound like much. True, it will eat stainless (it's stain less not totally impervious unlike the german Rostefrei (rust free---hah!)). But if you dilute it enough, it won't harm your pipes, particularly if you have PVC drain pipes which are pretty much impervious to dilute HCl. Stomach acid is a few percent, maybe even 10% HCl, as anyone with acid reflux will tell you, you want to keep that acid where the body is protected from it (the stomach, not the esophagus) but it isn't immediately dangerous to life with proper handling. Don't bathe in it, but don't overly fear it either. If I've used a lot of HCl, and I have iron and copper drain pipes, I will neutralize it with baking soda first to double "bomb proof" the dilution thing. This makes a lot of fizz (carbon dioxide) so use an over-sized container.

The problem is that almost no photographers have adequate ventilation and few have proper splash guards or respirators. The chemicals that most people are used to using in the DR are not really much of a concern, but HCl is a bit above that, and needs more respect than most DR people give their chemicals.

I use it very occasionally and in very small quantities, but I don't use it for a clear bath. That is introducing a lot of it in the darkroom where it sits in open trays, and there really are better ways to clear prints.

Oxalic acid is in rhubarb, spinach, and other 'bitter' greens like kale, etc. It takes a lot to ingest a lethal dose (8 pounds of spinach, if I recall correctly), so not really a concern, but it is a good enough excuse to avoid those things (if you needed a reason).


---Michael