Quote Originally Posted by Rudeofus View Post
I'll answer instead of Mark: Photo Formulary sells sodium metaborate which according to their MSDS is sodium metaborate 4 mol. This MSDS lists the formula NaBO22H2O [Na2B2O44H2O]

Likewise there is a reference on http://www.borax.com which lists both 4 mol (NaBO22H2O) and 8 mol (NaBO24H2O) sodium metaborate. So for all practical purposes I would assume that Mark means the 4 mol compounds as defined by these references: NaBO22H2O

The confusing names seem to come from the double compounds Na2B2O44H2O and Na2B2O48H2O
Confusing naming indeed. More confusing than the usual question of the degree of water of crystallization in compounds like sodium carbonate where at least if it's labeled correctly we get only one version, e.g. monohydrate, decahydrate etc.

So confusing, in fact, that www.borax.com have made a mistake in their product data sheet for the 4-mol. See page two, top right, where 4H2O should read 2H2O.

I wonder which version my sodium metaborate is (bought at Vanbar Melbourne). It didn't matter much with PMK because Part_B was pretty much a saturated solution and some people varied the relative amounts of Part_A and Part_B anyway. But in this interesting concentrated Xtol-like developer I would guess that the pH would be sensitive to errors in the exact amount of metaborate.