Quote Originally Posted by Photo Engineer View Post

I won't laugh, but one operation I will not do is filter a concentrated KOH solution. Too much chance of an accident, and the KOH usually ends up dissolving the filter paper. The CaCO3 is colloidal and can go through the filter paper.

Best use a sintered filter for this one, if it even works.

Yes, some not only goes through the filter, but very soon clogs it so that not much of anything goes through. I don't try filrering any more. I stir vigorously, let it settle, and stir again. After it settles, I decant most of the clear liquid as slowly as possible so as not to stir up the settlement. It's not the best way to prepare a really concentrated KOH solution, but I think it will be good enough for Rodinal. A gram molecular weight each of Ca(OH)2 and K2CO3 will produce 112 grams of KOH . I don't need more than 30 grams, which should be easilly gotten if I use enough water to make a 30% solution. It's theoretically more wasteful than filtering, but the ingredients are not very expensive and can probably be more easilly bought in some places.