A real formula

[Photo Engineer]

Silver halide is sensitized by adding thiosulfate at 1 - 100 grams / mole of silver present. Unfortunately, this level is based on grain size (surface area actually) and therefore unless you have electron micrographs you have to determine it by trial and error.

Gold is used a 1 part of gold salt / 3 parts of thiosulfate.

Don't use Dichromate.

PE

As a very kind person has noted, this post should read Thiosulfate is added at the rate of 1 - 100 mg / mole of Silver present. And it is based on Sodkum Thiosulfate Pentahydrate.

Sorry for this mixup.

PE

 

[kb3lms]

Add 28% ammonium hydroxide to B with stirring until a clear solution results.

PE,

At this point, how much ammonium hydroxide is used? I am ordering materials from the Formulary and want to make sure I get enough. Would I be correct in understanding that it is a fairly small amount?

Thanks!

 

[hrst]

For me, it was around 20% of solution B volume.

 

[Photo Engineer]

PE,

At this point, how much ammonium hydroxide is used? I am ordering materials from the Formulary and want to make sure I get enough. Would I be correct in understanding that it is a fairly small amount?

Thanks!

It really depends on batch size.

I use about 25 ml of 28% Ammonium Hydroxide for about 250 ml of emulsion, but this depends on quite a few things such as the "real" concentration of the Ammonia solution. It is subject to changes due to evaporation of NH3 gas. So, I order about 250 ml at a time and it lasts me for about 5 - 10 batches depending.

PE

 

[kb3lms]

Thank you for the info. Well, I have off between Christmas and New Year's so I am looking forward to making my first run soon!

 

[Photo Engineer]

An old style variant of this is in Baker 2nd Edition as a high speed emulsion. You may wish to look at that. However, none of these old texts really say how much Ammonia, and sometimes not even what kind (in modern terms). Baker used Degrees Baume for his Ammonia designation and you have to convert to percent. A real pain.

PE

 

[Kirk Keyes]

You can use lookup tables like from the middle of your CRC Handbook of Chemistry and Physics to figure out the Baume to percent conversion.

Or search the web...
http://www.hillbrothers.com/ammonia/pdf/AA-properties-1.pdf

 

[Photo Engineer]

Kirk, this can be done but there somewhere you will find a discontinuity in the way Baume was reported and you have to interpolate. At least that is what I remember. I had some problems and just finally guesstimted 28% because the values given in the BIOS and FIAT reports were at the high end of the charts. Which is 28% in terms of concentration.

And, BTW, just as British and US gallons differ, IIRC German and British/US degrees Baume differ.

PE

 

[lesm]

I hope this isn't a red herring, but the owner of one of the better camera shops here told me last week that 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? And for those interested in making their own formulae, what sort of stockpiles are there for silver nitrate?

 

[Photo Engineer]

Actually, due to the economy, some say that silver demand is up as governments and individuals try to buy enough silver for coins or to buy silver coins. Which is true? IDK.

PE

 

[MDR]

Les its very doubtful that Film manufacturing is the reason for closing the mines, it's more likely that some investors or funds are closing the mines to create a short supply and a rise in silver price.

Another thing just found this site selling ballistic gelatine http://www.gelatininnovations.com/pages/documents_ specifications.html would that be active gelatine, they specifically state that it's not food gelatine.

Dominik

 

[Photo Engineer]

I have no idea myself.

PE

 

[hrst]

would that be active gelatine

If you want active gel, just buy food grade sheets from the supermarket. I have had great results with that and it clearly is active and did the sulfur sensitization just as expected with this formula without extra steps.... Plus, you will get the same great uncertainty as in the old days .

 

[MDR]

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

Dominik

 

[Photo Engineer]

The brand and batch # will probably make some difference in the results with unrefined gelatin.

PE

 

[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/htmlgen.py?content=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