On KHCA and other wash aids, do you have any suggestions as to a starting point for soak times assuming continuous agitation (presumably optimal as with most photographic solutions)? - I've been using 3 minutes in the last week for 8x10" fibre base work prints.
On Gold toning: Tim Rudman (the lith printer) has suggested prints should be fixed after Gold toning, what is your view?
Tom On 12/07/2010 18:02, Richard Knoppow wrote:
----- Original Message ----- From: "Tom Kershaw" <tom@xxxxxxxxxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Monday, July 12, 2010 3:41 AMSubject: [pure-silver] Re: Using a selenium toner solution to test for residual silverHe is wrong. KHCA, and other sulfite wash aids, are very effective in accelerating washing. The chemistry was well explored at Kodak Labs. I will find the citation to the original Kodak technical paper but the patent explains things pretty well. KHCA is essentially a 2% solution of sodium sulfite (working solution) buffered to neutral with sodium metabisulfite. It also contains two sequestering agents: sodium citrate and EDTA tetra-sodium salt. These are to prevent deposition of aluminum compounds from the hardener in hardening fixer or magnesium and calcium compounds from the water. Kodak found that the anion of the sulfite was not important, ammonium or potassium sulfite is as effective as sodium sulfite. Other alkalies do have some ion exchange ability but are much less effective than the sulfites.Richard,Thank you for the informative response. Your comments on Gelatin pH and washing criteria cleared up a few points that are not always well explained. I do have a few questions:1. Some practitioners (e.g. Ron Mowrey) suggest that Kodak HCA isn't a particularly helpful treatment in a standard black & white printing sequence as it introduces more compounds that need to be washed out; do you take a view on this?2. From the tenor of your post do I take that the important factor with regard to washing thiosulphates out of the emulsion & paper is the total reduction of thiosulphates at the end of the process and not the split of wash times between pre-toning and after-toning? Therefore the paper can be tested for washing effectiveness without Se toning and then that time added onto the end of the process after toning, with a suitable wash or HCA stage between the 2nd fix and Se toner, which is not trying to remove thiosulphates but simply change pH towards neutral or alkaline?The amount of thiosulfate in the emulsion after all processing is important although toning will passivate the silver and help prevent the effects from decomposing residual thiosulfates. KRST does have some ammonium thiosulfate in it, in fact, its mostly ammonium thiosulfate, however, the concentration in the toner is relatively low plus there is nothing in the toner to cause binding of the thiosulfate ions to the gelatin or image silver so it washes out relatively rapidly. A treatment after toning with KHCA will further accelerate washing. Prints toned with sulfide or gold don't need treatment before washing.3. It was my understanding that gold toner is the "gold standard" also, but if selenium toning is to be the sole toning treatment used I had understood that protection was not even across the print; although Se toning as the sole toner does seem to be a standard practice as far as I can tell. Ralph W. Lambrecht suggests the use of Agfa Sistan stabilizer as a final treatment for prints, however I feel some degree of reluctance trusting this type of product fully, and wonder whether you take a view?There was never any research published on the effectiveness of Sistan. According to private correspondence with Dr. Douglass Nishimura of the Image Permanence Instute, an informal research project was undertaken there but never completed. There is some question about how effective Sistan is. It is sensitive to the concentration in the emulsion and instructions from AGFA were changed at least once. Excessive amounts of Sistan can cause sulfiding similar to excessive hypo. It is mainly potassium thiocyanate, one of the substances used in the old stabilization processes, with a wetting agent (Triton-X) added so that it can be used as a final rinse. Its advantage is that it causes no change in image structure, color, or density. However it was never accepted as a standard treatment for microfilm. Fuji also makes a stabilizer called Ag Guard which has been shown in research to be effective but less so than toning. I don't remember what is in it but its not the same as Sistan.Tom-- Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.
============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.
