And I can't disagree with you either.
I can only say that the variability may be on the micro scale of image quality in negatives and may not be visible unless you do direct comparisons or quantitative tests, and so you may not get the best out of your imaging process.
I know you are right when you say that certain impurities vary for human consumption that cannot be present in photo chemicals and vice versa. I've seen that before. Silver salve uesd for human skin in burn cases is not of the same purity as silver metal used for making emulsions and so on and on and on. I cannot give exact figures on effects nor can I list the possible impurities that cause these problems, nor can I give amounts that can be tolerated. I have run quantitative tests in the past to show that there are tolerable limits and intolerable amounts of many 'impurities' in photo systems. Thats about it.
"As an example, Detol contains bromide."
what is Detol?
never heard of that before...when I googled it I came up with a type of soap, but didn't see anything that seemed related to photography
Originally Posted by DarkroomExperimente
thanks, my typo-detector wasn't working
I think PE meant "Dektol", which usually contains KBr in its recipe and definitely in the packaged product.
The 20 Mule Team box says unequivocally "Contains no phosphates or chlorine." If it contains any sand, I have never seen it, and I think I would have if it were there. It has been used as a flux for brazing and silver soldering, and the borax bead that is well known in flame testing.
I still don't know how we are assured that the borax we buy from a photochemical supplier is any more pure than what we get in that box, or conversely, how we know that the box contains a less pure product for photo purposes. The MSDS, as we have seen in the past, only warns of hazardous materials, and may report such oddities as "Borax....100% +/-1%." Is there a test by which the supplier can be assured? Or is the world taking the other guy's word for it, who is just having a big laugh while he gets a jug of household borax, photo borax, assayer's borax, medicinal borax... all from the same barrel?
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So-Called! Photo Grade is every bit as much
Originally Posted by gainer
a Grade as is USP. Even today, I dare say, World
Wide each month tons of PHOTO GRADE chemicals
are being shipped. Dan
Patrick - While I don't have details on Photographic Grade chemicals, I do have info on ACS (American Chemical Society) Reagent Grade chemicals (which will say "ACS Grade" or "Reagent Grade" on the label. According to the 4th Ed of "Reagent Chemicals, American Chemical Society Specifications", sodium borate (aka Borax or sodium tetraborate) must pass specifications for the following requirements:
Insoluble Matter: not more than 0.005%
pH of a 0.01M solution: From 9.15 to 9.20 at 25C
Chloride: not more than 0.001%
Phosphate: not more than 0.001%
Sulfate: not more than 0.005%
Calcium: not more than 0.005%
Heavy metals (as Pb): not more than 0.001%
Iron: not more than 0.0005%
Differences from Photographic Grade, I don't know. I don't have the specs. But I suspect it is similar.
PE mentioned the following: Halides, Calcium, Magnesium, Sulfides. Halides may fall under the test listed for Cl, but Mg and Sulfide are not listed for ACS grade. The tests are generally easy to do, and only a few specify atomic absorption equipment, but being the gadgeter that you are, I'm sure if you got a copy of Scott's "Methods of Chemical Analysis" from the 1920, you could hack out a few of these tests at home. I think Google books has that online for one of the early editions.
Oh, and I understand that AR (analysed reagent) grade is ACS (or Reagent) grade that has had the batch analysed and the results of the analysis are printed on the label so that you can verify that your needs will be met by the results of that batch analysis.
Perhaps Mick could give us a list of the specifications on his bottle?
Usually the ACS analytical grade lists those contaminants most commonly found in a given type of reagent. Thus there is usually no analysis for something that is not usually found. A pro forma test is made but that is about it. So, you don't expect to see Tellurides or Selenides or Sulfides in Borax and so a simple test to show presence or absence is sufficient.
The ACS grade above is close to exactly photo grade. In fact we used ACS Analytical grade for almost everything.
Kirk, having that information is part of the solution. The other part is finding the analysis of 20 Mule Team Borax, since the argument at hand is whether the borax at the supermarket is good enough for most photographic purposes, which I take to mean any use where borax is specified as part of a solution for processing black and white film, but a particular grade is not specified.
In my three years of study of chemical engineering at WVU I did well in qualitative and quantitative lab courses. What got me to change to aeronautical engineering was physical and organic lecture and lab courses, a lecturer who didn't know how to lecture, a 21 credit-hour load, courting my future wife, and I forget what else, all in the same semester. I made the mistake of studying all night before finals. I drank tea that was so dark you couldn't see through it, brewed in a coffee percolator. The tea wore off suddenly about the time the exam began and I don't remember anything until the assistant woke me when time was up.