View Full Version : Selenium Toner (KRST) Yellow Tint

21-Sep-2010, 18:24
I routinely use KRST when processing paper. The bottles of stock solution have always been completely clear, just like water in clarity. But I have two bottles, the first of which goes into use tomorrow, which have a faint yellow tint. They are brand new. Is the yellow tint anything to worry about? Anybody know why the color differences? Thanks.

Gem Singer
21-Sep-2010, 19:18
The bottles are brand new to you, but they might have sat on a dealers shelf for a long time before you received them.

KRST contains ammonium thiosulfate (rapid fixer). I suspect that the sulfur in the fixer is beginning to precipitate out of solution.

Nathan Potter
21-Sep-2010, 19:33
I have a bottle that also has a distinct yellow tint. I think Gem may be right here about the sulfur precipitate. I can't tell if the color is a particulate that could be removed by a fine filter but if you are set up to do that you might try it. OTOH I doubt that the color would show up on your prints but you certainly don't want sulfur residue on the print surface.

When I get a chance I'll try filtration through a 1 um millipore filter.

Nate Potter, Austin TX.

21-Sep-2010, 22:09
Thanks for the info. I could not see any precipitate. The toner stock is not cloudy. Should I scrap the yellow bottles and keep the clear bottles? I don't want to waste paper and time. But I don't want to waste 2 bottles of toner either!

Doremus Scudder
22-Sep-2010, 03:27
For goodness sake, don't just "scrap" two bottles of (dangerous, heavy metal) selenium toner.

First, it is more than likely (99.99%) good. I use selenium toner by replenishing the working solution and never toss it. I have two gallons in different dilutions that are still going strong after more than five years. I seriously doubt that the stock solution could ever go bad. Do try it at least!

Second, if you ever do need to dispose of selenium toner concentrate, take it to a hazmat facility to be disposed of properly (or, send it along to me, I'll use it to tone prints with!). I'm sure that is what you meant when you said "scrap," but I just wanted to make the point just in case, or for others.

If you are interested in how I use selenium toner without ever disposing of any heavy metal, it's fairly simple: Just add a bit of stock to the working solution when toning times get to long for comfort to increase toner activity a bit. A precipitate forms (dissolved argentothiosulfites probably, which have reacted with the toner) and settle out making filtering through coffee filters or the like necessary. I filter before and after toning sessions. Keep your working solution, using and replenishing as needed. They never wear out. I have a gallon each of "strong" and "weak" toner for different papers (and, as I mentioned, they are both at least five years old).

If you must pour working strength toner down the drain (a bad idea in my estimation), at least use it to exhaustion first and then leave a few scrap prints in the solution overnight to scavenge as much selenium from the solution as possible before discarding it. This will at least minimize the environmental impact.

Hope this helps,

Doremus Scudder

Gem Singer
22-Sep-2010, 05:59

If you suspect that the fixer in the KRST concentrate is going bad, use a rapid fixer for your prints, and transfer the prints directly from the fixer into the selenium toner.

If you soak the prints in a hypo clearing agent (sodium sulfide) for a few minutes after toning and before washing, there should be no effect from the yellowing of the KRST.

I also have two old unopened bottles of KRST that have begun to turn yellow. Not going to scrap mine. No need to scrap yours.

22-Sep-2010, 06:16
Thanks for all the comments. I will be upstairs using it this morning. I suspect it will be fine and will post back if there are any problems. I was not going to dump it in the sink - probably put it in the garage in preparation for a future estate sale (I hope in the distant future).

22-Sep-2010, 07:20
I was under the impression the yellow tint was a change by Kodak...but couldn't find info to confirm...

I have two bottles one from 2005, clear liquid, and had been an opened partial since purchase...no signs of yellowing....and a new bottle recently purchased (from bh - 2009 lot) that arrived with a slightly yellow tint, and no signs of precipitate...

Recently finished the 05 bottle and began using the 09...and didn't notice any difference....


Arne Croell
22-Sep-2010, 09:20
If you soak the prints in a hypo clearing agent (sodium sulfide) for a few minutes after toning and before washing, there should be no effect from the yellowing of the KRST.

Just a small correction: You surely meant sodium sulfite as the main ingredient in HCA, not sodium sulfide - two very different chemicals with very different effect on your prints...

Gem Singer
22-Sep-2010, 10:04
You're correct, of course, Arne.

Please excuse the "senior moment".