Cheapskate project last night, that worked so well I thought it might appeal to other cheapskates out there!
I have a pot of rosin flux paste that had dried out to the point of becoming a little difficult to use. I don't use it often, but when I do, I want it to work...
Rosin flux paste is thinned at the flux factory with chemicals that are a little difficult or expensive to buy in small quantities, e.g. diethylene glycol dibutyl ether and other esoteric compounds.
In the past, I have tried to make flux paste thinner with isopropyl alcohol and other thinners, but the ones I tried were never really satisfying and in any case always ended up evaporating relatively quickly, leaving the flux just as hard as before.
Then it struck me: why not use a liquid rosin flux as a solvent for the partially dried paste? The idea being that the thin flux already has an appropriate type of rosin solvent in it...
So, while my wife was not looking, I went to work in the kitchen... I added a small amount of the liquid flux to the pot (one or two ml), then heated the mixture in the microwave oven for about 15 seconds, enough to melt everything - stirred thoroughly. Let sit overnight to solidify.
The result is awesome - soft, supple, beautiful flux! A miracle cure - absolutely worth the effort.