After several times of using the BMW small bottle of touch up paint it becomes thick and very hard to use it.
What is the solution? What kind of liquid should be used to make it thinner.

It wears out quickly if
1) exposed to air
2) bottle gets very cold
3) bottle gets very hot.

Only solution is to replace it, and keep it indoors except when used.. and when you use it, cap it immediately after use.

I don't feel like replacing, the bottle is more than half full.
It has to be a right liquid to make it thiner i mean even at the factory there was a liquid base than got mixed with.
I don't think this is a water based paint, it is more like oil based but also paint thiner does not sound right.

Laquer thinner, as opposed to oil based thinner (mineral spirits). laquer thinner aremore volatile. Typially contain a high flash solvent, xylene, toluene. Try a couple drops to start, add more to get it right.

Laquer thinner, as opposed to oil based thinner (mineral spirits). laquer thinner aremore volatile. Typially contain a high flash solvent, xylene, toluene. Try a couple drops to start, add more to get it right.
Is acetone the same thing, i added some of it and it did magic, now i have almost full bottle again and is thin like new.
Thanks a lot, your info really helped.