As Sodium metaborate (Kodalk) now seems almost impossible to buy in the UK (Silverprint no longer carry it and enquiries to those chemical suppliers who will deal with private individuals have drawn a blank), I have resorted to brewing my own using the instructions Mike Wilde gave in a post at APUG in 2007, which I'll quote in full below.
Using this has prompted a few questions for me which I would like to clear up - I stopped learning chemistry in about 1974.
My questions fall into two areas.
First, relating to mixing the solution as Mike Wilde outlines:
I use Sodium hydroxide bought on the high-street marked as 98% w/w, and Borax bought from a chemical supplier via eBay (it is almost impossible to purchase Borax otherwise in the UK); I
use deionised water
1. When he says "until the solution clears", is this to the point where it is "gin clear" or to the point where it's "mostly clear but vaguely milky still" or what? The solution I've just made has been standing for 20 minutes: there are a few grains of what look like Borax at the bottom of the vessel, and some sort of soft white wispy product has risen to the top of the solution. In between, the solution has that slightly translucent look one sees in (say) D76 stock.
Remember IANAC ...
2. I seem to have to add a LOT of additional hydroxide to get the solution to clear - perhaps 2 to 3 times the starting weight of 19g. I have no idea of course whether this is to be expected or not.
3. If I do go "too far" and start getting the translucent metaborate crystals forming, how badly off might the pH then be to be and how detrimental to the working of any formula might that make it (another piece of string question I know, but if it's .5 off that's rather different to being 2 off I assume)
Secondly, relating to substituting Borax and hydroxide separately into developer formulae:
4. For the purposes of the home hobbyist making the odd litre of developer, will the purity of the hydroxide really make much difference?
I do understand that developers are formulated to particular pH ranges, and that one cannot expect them to work as designed if the pH varies wildly from that expected.
But if I use hydroxide that's been in its plastic bottle under my sink for 18 months, am I likely to go terribly far wrong? (Yes, I realise the most likely answer to this question is "It depends ...")
(Please remember I'm in the UK, so it's not going to help me to say "You can buy metaborate from the Formulary for $5/lb", because I can't ...)