How to make a faster unwashed emulsion?

Cadmium can be added at either of 2 points in making an emulsion (Cl/Br). It can be added during precipitation or after precipitation, just before coating. The amount used is different for each case. In any event, its use has been superceded by organic compounds with low toxicity and low environmental impact.

Liquid Light still lists Cd in the MSDS and a number of European and Asian companies still use Cd (last I looked).

PE

Ryuji said:

Do you have that MSDS in PDF form? How recent is it?

Click to expand...

This MSDS is currently on Rockland's website. The link is: http://www.rockaloid.com/msds.html#LL

Thanks for all of the replies.

rongui

mmm apparently something is not working

I bought some pure ethyl alcohol and added 5 ml in a 125 ml potassium bromide solution with about 20 g of food gelatin. The bromide gelatin was stored in a light tight bottle in the fridge.

The next day I melted the gelatin and heated some silver nitrate solution (20%) to about >40°. After the gelatine melted I went in the darkroom and under safelights poured some silver nitrate in the bromide gelatin (at 1:1 ratio). I started with just 20 ml (10 ml gelatin + 10 ml silver nitrate sol.). I mixed the whole thing until became white.

I coated the papers immediately after mixing.

The sensitized papers didn't work though. When placed into developer without any exposure to light, they became dark brown colored (a "rust" tone). It goes without saying that for exposed papers happens the same. But the same happened with the bromide gelatin prepared with denaturated alcohol. So, perhaps denaturated alcohol wasn't the problem.

The recipe was the same as the emulsion that worked in the first place but didn't keep well for more than a few days. Except that now I used separate solutions for each of the two components and I have mixed them only before coating papers. Also, I didn't use tap water, but distilled water. Could be something wrong in the mixing stage? Temperatures of each solution?

I don't think the silver nitrate is bad... I used the same solution of silver nitrate for some very nice POP prints this evening and they were just fine.

I just noticed that when I poured the silver nitrate into potassium bromide some precipitate formed and was very hard to dissolve. It looked like ordinary silver bromide precipitate, but in the previous batches I didn't notice such bigger "grains" of precipitate. They partly dissolved at the end of the mixing stage.

It could be that there is a reducing agent in the paper you are using, or it could be that you have gone into silver excess. If you add more silver than halide, the emulsion will fog.

Without gelatin to 'peptize' the silver halide, the crystals will be very large and will settle to the bottom. The siver halide formed in the absence of gelatin or with too little gelatin will be very foggy.

PE

I said before in this thread: Ethanol is not going to prevent bacteria from breaking down gelatin molecules. 5ml in 125ml of ethanol is completely ineffective for this purpose. Get a better biocide or give up on the idea of pre-dissolving gelatin. Once the gelatin is deteriorated by bacteria, what you observed will happen.

Sorry for no posts in the previous days, I was a bit busy.

No real news so far, I didn't give up the idea of a homemade emulsion... I just figured out it's much safer to prepare the emulsion and use it straight away. I only wonder how long the coated papers will keep before fogging. If relatively large batches of coated papers are possible, then it's worth the effort of preparing a new batch of emulsion every time one needs it.

Maybe I will experiment a little with some unwashed chloride / "gaslight" emulsion. Should I follow the same rules as in the unwashed bromide emulsion? Does the fogging in unwashed chloride emulsions occur in the same way?

I've been successful in sticking commercial emulsion (SE1) to a glass plate. The subbing solution suggested in "Silver Gelatin" didn't work very well (it worked, but wasn't perfect and I had emulsion lifting in some areas of some plates). What works really well is artists' spray varnish (the ones designed for pencil drawings, oil paintings, etc. - windsor & newton is ok). Apply that on a very clean piece of glass and you got the perfect substrate for emulsion. I left a glass plate for over 30minutes in water and the emulsion didn't lift.

Making negative dry plates is very fun. Positives are a problem and I haven't found yet a good way of making them.

I've posted a fair chloride emulsion here before, and the ones in "Silver Gelatin" look reasonable.

PE