Sandy, every time you have a drink of wine, you probably have some food grade sodium sulifte. There are food grade carbonates and bicarbonates and these are not often checked for Calcium, but are checked for Arsenic, Lead and other ingredients such as other heavy metals. Photo grade might be checked for Iron and Cadmium as an example.
Patrick, Kodak sold Borax, Bromide and Carbonate and use them yet in their own chemicals within the plant. The prepared Kodak mixes use approved photograde. The Formulary Ammonium Thiosulfate is the same as what Kodak uses and many of their chemicals are of the highest purity. The drums are marked photograde.
In general, photo grade materials also include checks for insoluable matter, but food grade materials may not as long as the insoluables do not contain any of the harmful heavy metals and other items such as this.
Oh, and Patrick, if you want to get Kodak grade chemicals, try the Photographers Formulary.
PE
Choose what you want to do, but when one want to gain converts, a full disclosure and a vetting process is in order.
Steve
Let me reiterate. My motive is not cost, unless you add in the cost of travel or of waiting for delivery. I cannot buy photo grade borax locally, nor within 100 miles of where I live. So far as I can tell from a thorough search, Kodak does not sell borax, and probably wisely so, since there are several other sources. Dial (20 Mule Team) can provide the NF grade, which seems to be slightly better than Photo grade, and I could get from them a 25 kg bag, which I might be able to use if I live another 82 years. The grocery store that is 10 miles away has 20 Mule Team borax. I do not have to wait, sometimes as long as 2 weeks, for delivery. I have been using it in D-76 and similar developers for years. I described a method of removing soluble impurities 90% at a time, at the same time making a standard solution that is not susceptible to variation due to the unknown mixture of penta- and decahydrates. If I cold not get that borax, I would probably contrive a way not to use borax for my purpose. In fact, I have already contrived and published several ways. Why are these alternatives not just as threatening to suppliers of "Photo Grade" borax?
You know, you and Ron seem to have backed into your respective corners and neither one seems ready to budge on the issue.
Let me try and break the standoff, for some chemicals household versions available from grocery stores may be acceptable, others may not be, any changes in chemistry must be considered experimental and must be tested before being used for images that are important or critical. Sometimes the experiment will be successful, sometime it will be a failure. So mix up that batch of home brew D76 using 20 mule team borax. Now go shoot a couple of rolls of the cat sleeping or the dog acting goofy, and run those your home brew first.
You must have missed several of my posts.
I agree with you to an extent in that you can run simple tests with this chemistry, but in some cases, you can run into a "gotcha" with cheap chemistry and ruin your photos. You may not even be aware of the source of the problem as the developer or fixer may have been ok 9 times before.
See my analogy to the speeder. Someday you will be nailed by your chemistry if it is not up to par.
PE
So....... at what temperature does sodium bicarbonate transform into sodium carbonate?
Alan;
Your comment on XTOL is a non-sequitur here. The problem was unrelated to chemical purity.
PE
You have not commented at all on the random errors in measurement of borax caused by weighing even the highest grade in the presence of air.
Alan;
... In addition to that, Kodak had a packaging problem with the initial offering of XTOL which caused it to spoil on the shelf with long term keeping...
PE
"When is food grade chemistry OK for use for photography, and how can you test to make sure?
That really is the big question.
And the tests are generally not very complex for most of the tests. The catch there is finding a copy of the actual specifications that are used. Go to www.iso.org and search for what you are interested in.
http://www.iso.org/iso/search.htm?qt=10349&sort=rel&type=simple&published=on
They can be bought, online, for about 40-60 Swiss Francs or so for each test in question. I have one at home (I'm about 600 miles away right now from there) for photographic grade borax. I'm pretty sure Patrick has a copy of the specification as well. Perhaps Pat would be willing to test his 20 Mule Team and let us know if that box of borax does pass the specifications for photo grade borax.
If you don't want to spend that money one standards or have the time to do the testing yourself, let someone else do it for you and buy photo grade.
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