try using more vodka (or lemon extract - high in alcohol). Sounds like your not using enough liquid. Remember though that the alcohol is going to evaporate quickly so you have to keep adding more to your mixture as it will thicken up as the alcohol evaporates - kind of an on going process while your painting. Hope this helps.
I use lemon extract in an eye dropper, then I just add as many drops as I need to make it work. Sounds like maybe you didn't have enough liquid the first time and a little too much the second.
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