Re: Two carbon questions

MessageLoris,

absolutely, no problem with the approach. Instead of guessing how much you need to add to compensate for the exposure not reaching the bottom I could suggest a similar approach to find out how much is left on the print after development for a specific exposure time and dichro %. This would take additional tests but you wouldn't be dissapointed with your first estimate which maybe far off. But again it may be all right I wouldn't know, having no experience to speak of.

The reason I'm trying to model all of this is because I don't want to repeat tests every time I change my mind about the tickness, Dmax and or the relief I'd like to obtain. I know I'll have to do a few more tests the first time around but after that never again except when I change pigment but even then the number of additional test will probably be limited to just a few.

The amount Sandy suggested seems to be about twice as much as my extrapolated value which could mean 5% increase may be far from enough. If I recall correctly Sandy as plenty of experience and I would be confident starting with his numbers instead of mine (guesstimates).

Regards
Yves

  ----- Original Message -----
  From: Loris Medici
  To: alt-photo-process-l@usask.ca
  Sent: Thursday, April 13, 2006 9:43 AM
  Subject: 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 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 09:04:22 2006