ammonia process emulsions

I've decided to try making my own emulsion and have chosen one, but

recipe I'm using (in photographic emulsions by E.J Wall) is an ammonia

process method but the recipe doesent specify the strenth of ammonia

to be used, any suggestions?

SRAD (Single Run Ammonia Digest) emulsions are very difficult to control and keep from fogging. In addition, the formulas from Wall are very much less 'robust' than those from texts just 10 years into the future such as Clarke.

 

I suggest that you go carefully with anything Wall says, as a lot is left out. I have found it difficult to repeat anything from Wall even though I know a lot about emulsion making.

 

In any event, the ammount of ammonia to use is as follows:

 

1. Buy concentrated ammonium hydroxide such as sold by the Formulayr.

 

2. Add the ammonia dropwise to the silver nitrate until it turns brown or black and keep going with lots of stirring. Keep adding a drop at a time and suddenly the silver nitrate will clear and look like pure water. This is IMPORTANT. Going less than or beyond this time will ruin the emulsion.

 

3. At this point, there will be no significant ammonia odor to the silver nitrate.

 

4. Make the emulsion. In so doing, the ammonia odor will return due to acid-base neutralization. The emulsion will digest as per Wall's instructions.

 

5. Wash well. The ammonia is hard to get out. I use PA gelatin to do this. I also use an acid base cycle to help out.

 

6. The emulsion as per Wall will not perform as modern gelatins don't contain the sulfur compounds that old gelatin does so you must add a sulfur 'finish' to the operation to get any speed or contrast.

 

Hope this helps. I suggest you take my workshop at the Formulary in June or in NYC in Sept.

 

Ron Mowrey

erm, I'm no chemist so, "how much of what" information would be nice, or a point in the right direction to more modern solutions would be nice.

Ross;

 

Jim Browning gives a complete 'modern' emulsion formula on his web site. He makes his own Matrix Film for the Dye Transfer process.

 

That can be used as a starting point.

 

Usually the sulfur is added based on the surface area of the emulsion, and can only be determined by trial and error unless you have sophisticated equipment. The sulfur is added as sodium hypo or thiourea or sodium thiocyanate in very tiny amounts using 0.1% solutions.

 

The book "Theory of the Photographic Process" by Mees and James discusses this in some detail. There are no real texts out there, as this material has been considered very proprietary by the various companies.

 

Ron Mowrey

Ross;

 

Sorry, but the reference above to Clarke was incorrect.

 

It is Baker "Photographic Emulsion Techniques" and it is about 20 years 'newer' than Wall. It still does not detail finishing and relies on active gelatins, but using Baker will be a good start.

 

Ron Mowrey

I read both Wall and Baker closely but both books are full of errors and misconceptions. I wouldn't use them even as a starting point for emulsion making.

 

Ammonia is a decent ripener but the old technique to add it to silver jet is not very good, if you are looking for good speed, contrast and low fog. The grains made this way usually look like potatos (uneven, irregular, and rounded faces of the crystals) and not well determined octahedral or tabular grain shape. (Ammonia is usually not used for chloride emulsions, and people rarely make cubic AgBr emulsions.)

 

I use a blend of a thioether and thiocyanate as the ripener with good results, but they are also added to the kettle (or halide jet) in the growth phase. I figured that adding a ripener or anything that accelerates crystal growth in the nucleation phase is generally a bad idea.

Someone sent me an e-mail today asking about the post by Ryuji above. I hate to revive an old thread but I answered this person's note and I felt I should follow this up in the thread.

 

Thioethers used for digestion are not very easy to control. With ammonia, you can add acid to shut down its effects. You cannot do that with thioethers.

 

Thioethers and Thiocyanates added during the precipitation can cause chemical (sulfur) sensitization to take place during the precipitation. The work of Sheppard et. al. originally showed that allyl thiourea was the chemical sensitizing agent in old active gelatins and to get more modern repeatable emulsions the thiourea was removed from gelatin to get today's photograde inactive gelatins.

 

Allyl thiourea, thiourea and Sodium Thiocyanate were all used in the early days after precipitation to get proper speed and contrast with the inactive gelatins. They were eventually replaced by Sodium Thiosulfate. These were all added after digestion and ripening so as to keep the steps isolated and so that the effects could be isolated and controlled.

 

The idea that people rarely make cubic AgBr emulsions is not relevant to this discussion as any silver halide solvent added to the make would destroy a cube. However I would like to point out that Kodak uses cubic emulsions in many situations, and in fact their world standard emulsion is a cubic bromide.

 

Ron Mowrey