If objections to use of dichromates are based on valid environmental concerns regarding industrial waste disposal that is one issue.
If objections are based on concerns for one's personal health, that is another issue.
Having used dichromates in carbon photography for almost three decades, and carefully considered the risks, my opinion is that there is less risk involved with the use of dichromate in making gum and carbon prints than the risk involved dozens of activities that people engage in on a regular basis, not including smoking cigarettes and heavy alcohol consumption. Once the dichromate is in solution the concern is almost entirely dermatological, unless one decides to drink the dichromate.
I can understand why governments want to regulate and/or reduce/eliminate the use of dichromates. But for the individual making gum bichormate or carbon prints there is, IMHO, virtually no risk to health, assuming reasonable care in mixing.
Originally Posted by q_x
Sorry, this is not a direct reply to the question, but related to dichromates nonetheless.
I just started working on gum bichromate process and am now preparing chemicals. There's a problem with ammonium dichromate though. Upon dissolving in water (I'm preparing 10% sol'n), small filaments form in the solution. The filaments are dark green/brown in color. They are insoluable and soft in consistency and stick to the walls of the glass beaker. I am using distilled water, but this is the first time i used samples from this particular chemist, so I can not vouch for its purity.
Does anyone have an idea why these filaments appear? And does their appearance mean contamination of the dichromate solution?
I have prepared the solution under dim tungsten light, so exposure to light should not be a problem.
And Mustafa, if I'm able to eliminate this dark green/brown substance I can lend you some solution, so there, I had an answer to your question after all :)
But if you want to prepare it at home I suggest you get controlled air flow in your working environment or a gas mask from Karaköy. The particular brand of dichromate I purchased had some very fine crystals (normally the crystals are relatively large and easy to work with) which may pose some risks unless there is controlled airflow.
Can - I don't know what the filaments are, but I would bet if you just filter them out, the solution will work just fine. Is the solution itself a bright orange color?
There`s no problem with it.
Originally Posted by q_x
q_x please try those two links
And to think of the way we used to chuck it about in chemistry lessons at school - and as far a I know I'm still fine.
Thanks for the reply, the color is fine, bright orange. I'll filter the solution with a coffee filter when i get home.
Though I have minimal experience in the process, I suspect the filaments (for the lack of a better word) formed because of impurities in water. Does anyone have an idea on how impurities in distilled water may affect dichromate solution (and during the printing process)?
Originally Posted by Kerik
Thanks for the links, Paul.
Can: the things you're filtering (greenish brown filaments) are a thing left after exposing bichromate salts to light. It won't spoil your prints, just keep the solution in brown glass and in dark place if you dislike it. It is quite precious olive green pigment, but hard to use in bichromate processes due to its small particle size.
(1) It looks like can has got some impurity in the water (although there shouldn't be any impurity in the water, if it's really distilled water) or in the container. I agree with Kerik that as long as the solution itself is still bright yellow-orange, the filtered solution should be fine. (BTW, I've never seen anything like this in all the years I've been gum printing).
(2) Light doesn't have any lasting effect on dichromate by itself; there must be some other material to participate in the reaction. Without a donor material to participate in the reduction of the chromium the reaction doesn't occur; that's the role gum arabic plays in gum printing, is serve as a donor to facilitate the reduction of chromium. The crosslinking of the gum, which is the foundational principle of gum printing, is a collateral effect.
(3) As to the green filaments in can's dichromate being a precious pigment... well, I'm somewhat skeptical of that assertion, but would be glad to be enlightened, if it can be shown that this is the case. But since we don't know what the impurity is or how/whether it's reacting with the dichromate, it seems rather unlikely that we could say anything definitive about the product.
thank you all, g_x, katharine, kerik, for your fine answers.
Troubleshooting a new process turns out to be very discouraging at times, especially in an early phase, thank you very much for your answers. I'll filter the dichromate solution and give it a try. And in the future I'll find a more reliable source for distilled water.
the pigment comment is especially interesting
i'll copy paste the thread for future reference
Since q_x hasn't substantiated that comment, I'm going to assume it's not substantiable, any more than his statement that the green filaments are produced by the action of light on dichromate, sui generis. It just doesn't happen that way, as I explained.
Originally Posted by can
The kneejerk assumption one might make is that the green filaments are chromium oxide, but as I said, without knowing what impurities you're dealing with and how they're reacting with the dichromate, it's impossible to know that. There are, in fact, two chromium oxide pigments, neither of which is particularly precious; one is PG 17, chromium oxide green, sometimes marketed as "olive green" (although "olive green" usually is reserved for a mixture of pthalo green with various yellows and rose-colored pigments). Chromium oxide green is a dull green, weak pigment, not terribly useful in gum printing, and one of the cheapest pigments available. The other is viridian, PG 18, also a common pigment, not very expensive. There are no other green chromium pigments I am aware of, precious or not. But as I said, I'm always open to being educated, if someone has better information.