So I bought Humbrols Dark Green Wash about 3 weeks ago. Looked fine in the shop. However today when I opened it I noticed it's gone thick, cloggy. Even after I've stirred it around for quite some time. My other washes are fine.

My question is what ratio should I try to thin it out with? I tried thinning it out once, but ended up ruin my test surface which I had painted with a gloss cote varnish from Humbrol.

Or should I simply buy a new can?

Buying a new can may be the easiest option, but who can guarantee it is not as 'good' as the one you already have?

Try to add a few drops of thinner to it (no more then 1/4 of the volume you have in the jar/bottle), than mix properly and leave overnight. If there is a reaction, you'll notice changes in consistency. After that (positive response to thinning) you can dilute it with more thinner or leave it as is to thin immediately before application.

HTH, Paul

Thank you Paul! I will do this and tell how it went.

I would try adding Mr Color Thinner rather than enamel thinner.

I'm pretty new to thinning overall, what would Mr Color give advantages over a Humbrol enamel thinner?

Humbrol enamel thinner is nothing more than refined white spirit. Try Tikkurila 1050. I guess it is easy to find in Sweden. Mr.Color thinner is more aggressive, in addition to the purpose it is intended I also use it for paint stripping to repaint (and even reprime, as it removes the primer as well) my models. All you need to remove paint/primer from any surface is to rub it with a moistened cotton swab.

P.S. When I said 'mix' I meant 'stir' in my previous post!