Humbrol Paints

I am having a bit of trouble airbrushing Humbrol enamels atm. I was ABing an intake trunking, matt 167 dark gull gray I believe it was, and as it began to dry and cure the paint went milky, but only around panel lines and concaves. I have also had  a similar problem with matt 140 light gray. But not only does it go a little milky around lines and what not, but I also can't get a decent, consistent finish with it. It's always slightly grainy. I use humbrols' enamel thinner so I am not sure what it is that's troudbleshooting. Possibly my thinning ratio.

Any help with this greatly appreciated.

Your experience is odd . I also have used Humbrol for at least 20-25 years and is my paint of choise, specially the buffing metal cote ones. I have never had a problem stirring the paint in the small tins, just got to be careful. They brush on without brush marks and they cover on the first coat, which is great when painting figures or small parts. They also last a looong time. I have some that are 20+ years old and are still good.. 

I have been using Humbrol for about 25 years, and like anything else there is a learning curve.

It is fantastic paint, is about the most opaque paint out there, and must be stirred very very well, as the pigments are finer and hence a higher quality product. Many figure painters use it for this reason, and they are a picky lot.

You can absolutely stir the paint in the can....you must start slowly...and increase speed when it starts to look like paint. I would say a good solid minute or more of stirring a new tin.

If some of the base/paint gets into the lid you just wipe it out with a q-tip or two and wipe the tin down. Q-tips should always be on your paint bench within reach anyway.

Humbrol flat or Matte as they call it is dead flat.

If you're using a brush forget stirring.

Humbrol's containers are so small chances are you'll spill it all over your work table.

Use a small sheet of glass as a palette and pick out a lump of pigment with a toothpick.

Wet your brush with thinner and wipe off excess as you would for dry brushing then pick off a small bit of the pigment.

Humbrol's pigments are ground so finely this will work great.

With an airbrush, you can put the colours over to larger bottle to aid with mixing. 

Stir stir stir stir stir.  With any paint especially the humbrols i have found.

It may sound like a silly question, but have you stirred the paint thoroughly? If not, you need to stir the paint well, until there are no limps or strings sticking to whatever implement you use to stir.