RE: Two carbon questions

 
Actually I was planning to make small batches of glop w/different amnts.
of pigment and coat them onto paper (thickness = 1mm) to visually
determine the minimum amnt. of pigment giving the necessary (acceptable)
density (and use slightly more pigment -> 5% more for instance - since I
won't / shouldn't expose deep to the bottom). A ballpark figure will
save much time in this type of testing... Do you find this approach
logical?
 
Regards,
Loris.

-----Original Message-----
From: Yves Gauvreau [mailto:gauvreau-yves@sympatico.ca]
Sent: 13 Nisan 2006 Perşembe 15:34
To: alt-photo-process-l@usask.ca
Subject: Re: Two carbon questions

Loris,
 
I can't help you much on most of this but I have been thinking lately
about how much pigment to use in g/100ml (or % if you prefer) all this
base on a constant Dmax I want to achieve whatever the tickness.
 
I came up with the following formula:
 
Pigment concentration = K/Tickness
 
where
Pigment concentration you need is in grams/100ml
K is in milligrams of pigment per cm^2. This value is the amount of
pigment in milligrams you need on a 1 cm by 1 cm square such that the
reflective density is what you want to achieve as Dmax. You will need a
bit more then this depending on how deep your exposure will reach. I
still have work to do to factor relief, exposure and % dichro.
Tickness (wet) is in millimeter (mm)
 
You can adjust K such that it will take into account that only part of
the tickness of the emulsion will be left on the final print and thus
reducing Dmax. From the recipes given here and elsewhere K would seem to
be around 3 mg/cm^2 which give pigment concentration ranging from 2 to
12 grams per 100ml for tickness ranging from 0.25 to 1.5. Based on these
number to get 1mm wet tickness you would need 10 grams per 100ml but but
but this doesn't account for relief and it isn't even base on actual
measure of densities.
 
Regards
Yves
 
 
 

----- Original Message -----
From: Loris <mailto:mail@loris.medici.name> Medici
To: alt-photo-process-l@sask.usask.ca
Sent: Thursday, April 13, 2006 7:12 AM
Subject: Two carbon questions

I plan to make a normal contrast tissue using indian ink. I want to
prepare the gelatine + sugar + ink solution beforehand (will coat the
tissue later). Sandy's carbon and carbro book says that the gelatine
solution can be refrigerated for later use (remember reading this
somewhere else too). I tried to refrigerate gelatine solution once
(about 250ml, 10%) and after about 2-3 weeks in the fridge, the water
was evaporated completely leaving only dry gelatine in the bottom of the
vessel - it was fun to play with the dry gelatine disk later ;)
 
1) Does it mean that I have to fridge the gelatine solution in a
hermetic container? (I guess yes but I want to hear others would say...)
 
2) Won't heating the gelatine solution before coating or leaving it
about 2 hours in a warm water (45C) bath to have the bubbles expelled
(after adding the pigment and stirring vigorously) reduce water in the
solution (due evaporation) considerably? How this will affect the
working characteristics of the solution? Am I thinking too compulsively?
 
I plan to start with batches of 500ml... I aim for a tissue with normal
contrast / moderate relief. (Any suggestions for pigment quantity? I
want to make a tissue with 1mm wet thickness.)
 
TIA,
Loris.
Received on Thu Apr 13 07:37:58 2006