From: Katharine Thayer (kthayer@pacifier.com)
Date: 07/25/03-02:58:09 AM Z
Hi Sam and all,
(See comments embedded throughout quote below):
stwang1@bellsouth.net wrote:
>
> Hi Dave,
>
> If I may jump in here, here is my way of using dry ammonium dichromate: I add water to
> gum to achieve the viscosity I need, add pigment till the color looks right, THEN add the
> required amount of dichromate powder. This way the viscosity and concentration of
> sensitizer are dealt with separately, and it will let me SEE how much pigment I need to
> put in. I understand this is a slightly different procedure as that used by Stuart.
>
> Another reason is that I prefer to use minimum amount of dichromate to do the job. I
> believe I use about 1/8 of what many others do.
Please bear with me while I try to understand this. Not that I'm ever
going to switch to this method of mixing, but I'm the kind of person who
needs to understand even things that aren't useful to me,
unfortunately. Here's what my problem is: unless I'm printing a series
of really huge prints, the emulsions I mix are almost always 5 ml or
less, often 2 ml or less, total gum, dichromate and water. But let's
use 5 ml as an example. 5 ml of emulsion, the way I most often mix it,
at 1:1 gum to saturated ammonium dichromate, would contain .675 grams of
dichromate. That's already smaller than I can measure with the equipment
I have, and when you start cutting that down, you get into extremely
fine measurements. 1/8 of .675, to use your estimate above, would be
.08 gram for example. For someone using such small amounts of emulsion
as I do, it would be impractical to work with dry powder; you'd have to
be using just a few grains of the powder, and if those three grains
didn't get just absolutely ground up to smithereens, your estimation of
the concentration would be off.
On the other hand, as Dave and Joe and possibly others have suggested,
the same end can be accomplished by using a saturated ammonium
dichromate solution and simply using less of it. One could get .08 of a
gram of dichromate, if one wanted that small an amount, into the
emulsion more accurately, quickly, and neatly (I say this having spent
half an hour trying this "dry dichro" business for myself yesterday
afternoon and finding it messy and time-consuming, and also finding
that in spite of sincere efforts to grind each grain, I was still left
with undissolved particles of the stuff in the final emulsion. A good
mortar and pestle would improve that, of course.) by simple measuring
out about 1/3 of a ml of saturated solution (an amount much easier to
measure accurately than .08 of a gram of dry powder, in my estimation).
So I'll add my voice to these others: what am I missing?
Another thought: according to Ed's notes, Melvin uses 10 ml of gum plus
2.5 ml water for an 8x10 print. That's a lot of emulsion for an 8x10
print, and I suspect a good deal of it ends up in the roller to be
washed out, unless this foam roller is a lot harder than I'm imagining.
So then there's the consideration of all that excess dichromate and how
to dispose of it properly.
Yes, that means I need to use it with
> negatives of a lower density range (lower contrast), not a bad thing since that means I
> can print my negatives on the cheaper overhead transparency films (as compared to
> Pictorico).
Ah, that explains why you and I differed about the FreeStyle laser
printer material. That was you, wasn't it?
>
> Yet another benefit from the lower amount of dichromate is that less is dumped down the
> drain (and damage the environment).
I agree, and I'm all for that.
>
>
> I believe I have mentioned all of the above before, but perhaps no one noticed.
>
I sympathize with you totally about no one listening to what you say to
the list. But how long ago was that? I already knew your name when I
came on the list in 1998, because I remembered the prints that were
included in Phil Davis's article in Photo Techniques, (was that 1995 or
1996?) so I've paid attention to everything you've had to say, and I
don't remember this.
Thanks for this great discussion,
Katharine
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