RJW quote-
'if you are using enamels you can use white spirit (big bottle for a couple of quid from wilcos) or a few other things you can use...il let richard or barry explain all them. if you are using acrylics it is best to use acrylic thinners (some people use water) which you can get from model shop/hardware store'
Be a bit careful here as some of the cheaper white spirit is like refined diesel oil,my advice is to go for a good quality white spirit for mixing your paint and use the cheap stuff for cleaning the gun,if you work in a confined space then use Sansador,this you can get from art shops and is a good quality artists thinner for use with enamels or oil paints,the effect on drying of the paint revolves around the solvents used in the paint,always try paints with a bit of thinners before commiting to the
airbrush as some colours do not mix properly,a good example of this is
Revell paints,these are formulated differently and some thinners will not mix with them.
Although I have not tried it myself some modellers use ordinary cellulose thinners for painting,but once again go careful as used on bare plastic it will certainly attack the plastic,use Halfords white/grey acrylic primer first should you go that route,the Halfords primer is an excellent product and will detect any blemishes which can be carefully sanded out with wet and dry paper prior to final paint being added.
Just go careful and use that paint hack model that I have mentioned here many times.