Source: Blog on DIY Flux

The above Link is in my opinion one of the best, strait-to-the-point explanations and insights for DIY Flux.

I have tried it myself with a 5% solution (5g/100ml) of colophonium in isopropanol.

The solution is quite liquid, but when aplied, the isopropanol dries off quickly and leaves a thin layer of colophonium on the solder pads. To solder with this solution is kind of a revelation. Almost no smoke at al and clean, shiny solderjoints.