[alt-photo] Re: ammonium dichromate

[Christina Anderson]

One semester I mistakenly used 2 tsp ammonium dichromate in 100ml instead of 3 tsp I normally do (duh-I remembered my "kitchen" formula wrong). Now that is a huge difference. I didn't notice any change in practice (like all of a sudden my layers were sloughing off), so I think worrying about half a gram is not as necessary as you may worry about.

Years ago we had this discussion of percent of dichromate. I had heard Suzanne Izzo used 2.5% dichromate, and so for a year or two used I used and calibrated a 7.5% and then went to a 15% which I use now (easier to remember when diluting full strength am di which saturates around 30%). I theorized that the dichromate hardening wasn't as "straight line" as we might think. Boy did that start a "discussion." I still believe that.

I think in carbon printing where you are using much smaller amounts of dichromate you might notice a difference being off half a gram, but in gum my bet is being off half a gram won't make a difference when you are using 10% pot di or over 7% am di. And I've probably calibrated 100 PDN curves in gum over my practice, so much so I can do it in my sleep or at least while watching TV.
Chris

Christina Z. Anderson
christinaZanderson.com

On Jan 31, 2012, at 9:15 PM, Dave S (fotodave) wrote:

> Well, the label says 0.5 to 3.0% wateren it is not precise, you cannot
> be very precise either.
> 
> I believe the percentage is percent weight. With 3% water, the percentage of
> dichromate is 97%, or 0.97. If your formula needs 15gr dichromate, you would
> change it to 15/0.97 = 15.46gr.
> 
> But if the water is 0.5%, the dichromate is 99.5%, or 0.995. For 15gr
> dichromate, you would use 15/0.995 = 15.08 gr.
> 
> So your new formula would need 15.08gr to 15.46gr dichromate per 100 ml
> water. I don't know if you need to be that precise.
> 
> If you really feel you need to make such adjustment, maybe you can use a
> value in between 0.5 and 3.0, say 1.75%.
> 
> 
> Dave
> 
> -----Original Message-----
> From: alt-photo-process-list-bounces at lists.altphotolist.org
> [mailto:alt-photo-process-list-bounces at lists.altphotolist.org] On Behalf Of
> jusdado
> Sent: Tuesday, January 31, 2012 3:46 PM
> To: The alternative photographic processes mailing list
> Subject: [alt-photo] ammonium dichromate
> 
> Hello to all
> I have bought a new lot of Dichromate Ammonium, but their aspect is
> different to the one that I use. It is not crystallized. It is powder. I
> check that in the label says "moistened with 0,5-3,0% of H2O PRS. I imagine
> that I will be able to use it, but the solution will no longer be same.
> For example: i make solution to 15%, but now..... what quantity of
> dichromato and waht quantity of water to make the same solucition to 15%?.
> Thank you and pardon for muy English, text translated by computer.
> 
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