A real formula

[hrst]

Thank you for the responses, hrst since you're from Finland what Gelatine Brand are you using?

Dominik

Local brand "Meira", I contacted them once and they told me they import it from Germany and that the batch analysis shows sulfur content of < 50 ppm and that this is relatively constant between batches.

[MDR]

Thanks

[kb3lms]

An old style variant of this is in Baker 2nd Edition as a high speed emulsion....PE

Is there a copy of Baker's text available online anywhere? I'd be interested in looking at that.

[dwross]

Hi,

The link on this page has a couple of affordable options for Baker. Great Christmas reading!

http://thelightfarm.com/cgi-bin/html...tent=22Aug2011

d

[Photo Engineer]

Denise;

Very good collection. I would like to add that Grant had to rely on Hill and others due to the fact that there were few publications allowed and those formulas were specifically selected for publication. The work published, in 1965, came from work that was current in about 1945.

In that work you put up, you will see a very early version of the coating block and coating blade that i used in training and later re-created for my current work on emulsions. The last variety at EK had vacuum hold down, hot and cold tempering capability and were used to coat strips of film up to about 14" in sizes from 35mm to 120 to 4x5. You could even get 5x7s with skill. You could get 2 4x5s or 2 35mm x 12" strips from each sheet of film.

PE

[kb3lms]

Thanks, Denise. After the new year I will have to see about getting a copy of Baker on CD.

Hmm, PE, vacuum hold-down. You just HAD to put that idea in my head.

[cmacd123]

I hope this isn't a red herring, ..... silver mines all around the world are closing down because of the shrinking film market. He said film had been one of the main uses for silver for decades.
Any truth in this?

I am in Canada, and so the business pages regularly talk about the mining industry, Silver is generally found with Copper, and sometimes other metals, so often there is not a "silver" mine per-se.

The photographic industry when it was in high gear regularly recycled much of the silver, as it is all left at the lab when you process colour film. I recall a stock seller trying to create panic years ago by saying that industrial demand was greater than the amount mined, impling that one would make a killing by buying a nice Silver wafer and waiting for the supply crunch.

As far as demand, the european Union has a policy called RoHS on the electronics industry, requiring the use of Lead free solder. Typical solder has been a mix of Tin and lead, trying to use pure tin results in teh growth a "Tin Whiskers" over time, so the lead free solder generally contains some Silver.

There is a big push to collect "e-waste" for recycling, Noranda (now Xstrata) just grinds it up and puts it though the smelter at one of their Mines as the smelter is already set up to separarate out the metals... http://www.norandarecycling.com/commodity_pro.html

[JMB]

Most silver has impurities in it that will make it unusable for photographic emulsions. It would depend on the silver and on the nitric acid. Reaction of silver metal with nitric acid IIRC, requires red fuming nitric acid as silver is a noble metal. RFNA, as it is called, is rather hard to get and gives off very toxic fumes.

PE

Two questions:

1. Is there some way to test the emulsion suitability of a particular source of silver nitrate before actually putting it to the pudding test? If the seller claims 99.8% (concentration or purity, I guess) is this a sufficient or at least hopeful indication? [The claim actually seems a little extravagant to me, but I am not a chemist].

2. I have run across several references to the use of cadmium in discontinued paper emulsions. For example, many photographers liked a Forte paper, which apparently contained cadmium. Do you happen to know the source or sources of cadmium (generally) in an emulsion? In other words was it cadmium nitrate or cadmium bromide or some other source? And at what step in the emulsion making process was it introduced into the emulsion?

Well, I guess that's 2.5 questions. How many am I allowed?

Thank you! --Joe

[Photo Engineer]

Joe;

1. It depends on the impurity and the emulsion. And no, you cannot tell before hand. We used 99.99+ at EK, but I use straight Analytical grade which IIRC is a bit better than 99.8, but in any event with the work we are doing you will see speed and fog fluctuations. That is about the size of it. In real production, a variation of 1/2 stop is a disaster, but I suppose that we can live with that. Right?

2. Cadmium is used with Ag/Cl/Br emulsions to adjust curve shape. It has little if any effect on curve shape on other emulsions but there is some toning effect. So that is the primary use outside of Ag/Cl/Br emulsions. Cd can be added either during the precipitation or afterwards just before coating and after washing. The salt used depends on the emulsion. If you make an Ag/Cl/Br, you may not want to add a halide salt but rather may want to use the nitrate. OTOH, if added during pptn. you may want to use the corresponding best halide salt and add it with the alkali metal salt. Cd is used in massive quantity in some cases and in tiny quantities in others. It is VERY toxic. Have fun.

A side note to those here who poo-poo the idea that Photo Engineers are useful and denigrate our "science".....I ask them, could they answer these questions? You all know who you are! I hope you read this!

PE

[JMB]

Thank you! And give 'em hell, PE. I'll watch your back! --Joe