This section is from the "Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1922 " book, by Aristo Motto. Also see Amazon: Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1922 .
A GREAT many photographers adhere to their formulas religiously in making up their developers but never question the quality of the chemicals they use. Of course we do not mean to infer that the photographer should test each lot of chemicals he purchases but rather that he should know that they have been tested and that they come up to the standard adopted by the manufacturer who worked out the formula that is recommended for use with his products.
Aside from the developing agents themselves, the most important ingredients of developers are the sodas. One might say, sodas are sodas, and so they are, but they are often much more. If you were to analyze a sample of carbonate of soda and find that it contained 75% carbonate you might reasonably wonder what went to make up the other 25%. Possibly you would find that the 25 per cent of impurities was detrimental to the developer and possibly not. But if the formula called for one ounce of pure carbonate of soda and you used one ounce of a 75% carbonate, your developer would be 25% lacking in carbonate.
You know enough about developers to know that a 25% error is enough to throw the solution out of balance and produce a poor result. And yet in buying sodas indiscriminately it is not at all unusual to encounter carbonate of soda that does not test 80% carbonate. Naturally you would have to buy such a soda at 20% or more below the price of a pure soda or you would be paying too much for it.
It might be interesting to know that the large motion picture consumers of chemicals base the value of a soda on their laboratory test of its purity. If it tests 80% pure they know that one hundred pounds of that soda contains only 80 pounds of pure soda and if they buy it they pay for it on that basis.
That's laboratory control in buying.
Laboratory control in manufacturing and testing is the same in priciple but applies to chemicals that are manufactured, sold and used. We exercise a strict laboratory control over all chemicals bearing the Eastman trade mark.
You are familiar with the Eastman Tested Chemical seal. When you see it on a bottle or tin of Eastman Carbonate of Soda you are assured that the soda in that package is 98% pure carbonate. It is not 99% one time and 97% another - it is 98% all of the time. Laboratory control means just that - dependability and uniformity.
Eastman Sulphite of Soda also tests 98 1/2% pure sulphite. Elon, as we make it in our own chemical plant, is the pure monomethyl paramidophenol sulphate. The same chemical can be imported and sold under other trade names but it can not be better than Elon and in some cases is not so good. Strict laboratory supervision insures Elon quality and uniformity.
The same laboratory control applies to Pyro which we manufacture in large quantities. All of the other chemicals bearing the Tested Chemical seal which we manufacture, refine or buy for our own use and for sale, must meet our laboratory standards which are based on the quality necessary for the best photographic result.
When you see "1 1/2 ozs. E. K. Co. Carbonate of Soda" specified in a developer you can be sure there is a reason. The reason is that that formula requires 1 1/2 ozs. of a 98 1/2% Carbonate of Soda - no more and no less. The formula is based on sodas of that quality which makes it necessary for the formula maker to be specific.
Laboratory control is your protection and is expressed in the Tested Chemical seal which is the mark of certainty, uniformity and satisfaction in photographic chemicals.
Service is something which makes even the pessimist say "Thank you". It's the entrance of the personal touch on the otherwise purely business transaction.
From An Eastman Portrait Film Negative By Thos. H. Ince Studios Culver City, Cat.