hazy 2-color

[Steven]

Hi Steven,

Thanks for the update. Dye-sensitized DCG is tougher than regular DCG. Sometimes I've gotten results which were just as bright as my earlier blue-exposed DCG, only to find out that I couldn't repeat it. Adding color is tougher still. I work during the daytime, so I've also had some very long days (in your case, nights)

I've attached a paper on dye-sensitized DCG (apparently the first one by Graube in 1973) in the pdf input section. Not that it's necessarily relevant to your tests, but sometimes a paper can have a detail which makes it useful.

Thanks for posting the paper Joe.

Interesting that two IPA baths at 50% are used, one at an elevated temperature - I must give that a try.
Another thing I noted was they suggest prehardening gelatin coated plates using Kodak rapid fixer.

I don't know much about chemistry (moles), or the dye being used, but I do have some TEA.

I have just sensitized another couple of plates with my mix.
One with bovine gelatin and one with pig skin gelatin.

What sort of swelling bath temperature do you use with your MBDCG?
In the tests that I did, I had to push it up to 30C before I had any sign of milkiness.
I wonder if my gelatin is too hard.
I did wash the plates under cold running tap water for 20 minutes or so to get all the TMG and dye out.
I know that a long soak in cold water can cause the gelatin to resist swelling, even at an elevated temperature.
Maybe I should try using the first washing water at ambient temperatures.

Steven.

[Joe Farina]

Hi Steven,

My swelling bath for MBDCG is usually around 30C.

In the past with MBDCG (Jeff's/Zhu's), I've had to wash carefully (usually for 1 minute only, plate submerged face-up in a bowl, under cold tap water, with a sink-sprayer being used to agitate the water on top of the emulsion). My gelatin is usually quite soft, I am working on methods to harden it after exposure. My layers that have been washed "too hard" show a white "frosty" look which is similar to "milkiness/branches" but slightly different. Your gelatin may be harder, so this may not be a problem for you.

It's good you're doing a side-by-side test with A and B gelatin. This should be helpful.

With regards to getting the dye out, a sodium metabisulfite and aluminum sulfate solution should do this in a minute or two (or just the plain sulfite, probably). At least with Jeff's/Zhu's MBDCG. I don't use fixer, the above combination works well for me. The alum can be left out, but I've had better results when it's included.

[Steven]

Hi Steven,
With regards to getting the dye out, a sodium metabisulfite and aluminum sulfate solution should do this in a minute or two (or just the plain sulfite, probably). At least with Jeff's/Zhu's MBDCG. I don't use fixer, the above combination works well for me. The alum can be left out, but I've had better results when it's included.

I tried a 2% solution of sodium metabisulphite with my first plate. I didn't use any alum hardener.
With my second plate, I followed Jeff's processing procedure. The plate came out very clear right up to about 27C swelling bath temp.

Which alum do you use?
I have both aluminium potassium sulphate and aluminium sulphate.
I will keep trying with dip and shoot, but may give coating a plate with sensitized bovine emulsion a try (pool on glass) just to see if it's dip and shoot causing the problem or the fact that I'm not using the proper TMG. I don't have a laminar flow work area, but it will only be a check on the chemistry.

Many thanks,
Steven.

[Steven]

aluminum sulfate