U of S | Mailing List Archive | alt-photo-process-l | Re: Do dichromates change with age?

Re: Do dichromates change with age?


Thanks for the info. It's probably something else - with gum there are so many variables! I might compare it with fresh stock though, just to be sure.

... and


Keep the moldy slides away from the rest of your stuff! In a different building if possible! With that many slides and negatives you'll definitely need to sept up something faster than a scanner. I would rig up a dslr copy devise, like a good macro lens or an enlarging lens on bellows, and zip through them quickly.

I've found some of my old negatives silvering out. Not fun trying to rescue them either.


On Jul 14, 2008, at 10:24 AM, Loris Medici wrote:


The page above says: "...Shelf Life: Unlimited in tightly closed

What I understand from this (and the previous page) is that heat +
humidity is definitely a factor affecting shelf life of dichromates.
Contamination also is an important concern. I purchased my Ammonium
Dichromate 5 years ago and it acts the same. (Yes, I know that's nothing
close to 20 years!)

I remember reading someone (British?) using NH4Di (maybe it was KDi) as
old as 30 - 40 years in the list archives but I'm not sure...


14 Temmuz 2008, Pazartesi, 5:01 pm tarihinde, sam wang yazmış:
Hi Loris,

The bulb is quite new, and I haven't noticed any speed loss with
palladium. The integrator on the Amergraph reads UV, so that's the
reason I replaced my old NUARC with it (integrator in the NUARC reads
visible light).

There are many other possible answers. Just wondering if dichromates
could lose potency.


On Jul 14, 2008, at 9:44 AM, Loris Medici wrote:

Hello Sam,

A question: does your unit have a light integrator? If yes, by saying
"longer exposure time" you mean "more units" right? If not (more
then could it be that your lightsource is getting weaker somehow
due bulb wear and/or voltage fluctuations)... Have you absolutely
out probable problems about electricity / integrator / bulb ect.?


14 Temmuz 2008, Pazartesi, 4:30 pm tarihinde, sam wang yazmÄ ±Å�:
Has anyone come across any data about whether dichromates losing
speed, or effectiveness?

My jar of ammonium dichromate is probably over 20 years old (yeah, I
use very small quantity in gum printing) and it appears to suddenly
need longer exposure time. Doesn't make sense, especially since I'm
using an Amergraph printer for exposure. Humidity and everything else
has been kept fairly consistent.

Anyone else has similar experience?