2 problems:
1) Air brushing with enamels thinned with turps substitute often produces a darker hue then the same paint applied with a brush; this becomes obvious when touching up with a brush - any thoughts?
2) Have recently experienced 'crazing' of enamel finish when applying a second coat, even after 3-4 days of drying for the first coat - has happened with 'COLOURCOATS' paint thinned with turps substitute but may happen with other makes which I have yet to try.

Does the "turps" have a tint to it of any kind? If it does that will darken any paint slightly. Around these parts there's a clear turp and one that's ever so slightly tinted yellow.
The cracking might mean too thinned out or incompatibility...I try and use the paint manufacturers recommened thinner when possible for best results. If I try using something different I test it on an old beater kit for correct ratio and coverage.
I use lacquer to clean everything up no matter what kind it is...the lacquer cuts thru anything which is good for cleaning. I use water for the acrylics as a thinner and enamels get thinned by "paint thinner"{2 parts paint/1 part thinner}...any lacquer I've sprayed has been thin enough to not need thinner{alclad}.

Thanks for the prompt reply. The turps has no colour whatsoever. I have wondered if air brushing more coats (I have completed 3 to 4) would lighten the colour. I am painting over a light gray primer. I think I will take your advice and use recommended thinners. Not sure about incompatibility - did you mean of the thinners?

Why would you be thinning enamel paint with turpentine (or as you say, a turpentine substitute)? Is this a method you've seen elsewhere?
Generally speaking, turps and their substitutes are intended for oil paints which are not the same as enamels. I suspect this may be your problem.

As suggested, try thinning your enamels with enamel thinner. When using Humbrol or Testors/Model Master paints I've had the best success using their respective thinners but have also had good results using cheap store brand paint thinner (mineral spirits).

Give it a try and let us know if your issues clear up.

Mark

Can't recall exactly where I picked up the use of turps as a thinners but, from now on, I'll give it a miss. Thanks for your response... I'm still on a fairly steep learning curve!

Turps is also a very harsh solvent (turps in the US may not be the same thing) and I wouldn't use it as a thinner regardless of paint type.

What is called 'Turps' in the UK is, in fact, a turpentine substitute and is sold as such. It is normally used for thinning oil-based paints and cleaning paint brushes. I agree with the earlier posts that I should switch to propreitory enamel paint thinners.
However, I'm still puzzled over the difference in hue between air-brushed and hand-brushed paint where the latter dries noticeably lighter- Have epxerienced this with a range of enamel makes and colours. I can't see how this problem is related to using turps as a thinner since the turps is absolutely colourless, but, I'll experiment and see what difference using a dedicated enamel thinners makes when air-brushing then hand-brush touching up afterwards.
Thanks for you help, it is much appreciated.

Hi Allan
Agreed with the above members, I would not use turpentine to thin enamel paints for airbrushing.

Try to stick to the proprietary thinner for the brand.

Turpentine and substitute turpentine differ in thier sulphur content and this effects how they react with various paint types.

Secondly, bear in mind that when you lay down paint with a brush it is invariably thicker than spraying with an airbrush and this could lead to the variiation in colour.

Good luck with your modelling.
Regards
Garth

I agree with the others, sounds like a compatibility problem with the "Turps" and the enamels.
I use Humbrols thinner for my enamel washes, as I find it to be an extremely mild thinner, and very low odor. (I rather enjoy it's odor--- much better than the lacquer thinner I use for thinning enamels for airbrushing! )

Also be careful if you are using Model Masters enamels, as they actually do have two thinners, their "AIRBRUSH THINNER" is way too hot to use for making washes. And don't confuse their "Brush Cleaner" for a thinner.
Any kind of crazing is a sure sign that the thinner being used is too hot, and you will need to find a much milder one. Also a clear acrylic coat applied before the enamel washes will help protect the previous layers of enamels. But again, any type of crazing is a sure sign that the thinner being used is way too hot.

Thanks to all of you for the advice which I will certainly heed

Hi Allan
Try and find some Humbrol enamel thinner ... Ive been using this for years and never had any problems.
I agree with Garth ... Sprayed on paint is a lot thinner than painted on paint, and could explain why the hue looks different.