Are these new tins, that sound slike its been contaminated. I have used Xtracolour and Humbrol for years, comes in the same tin and is apparently made in the same factory, and only had issues with the paint gelling if its old.
When Humbrol went to China for their production, there were some quality control issues. That gelled paint seemed to happen with the Chinese made paints. But thankfully they corrected that, changed their production location, and their paints are back to their usual performance, in my experience. Sometimes you do have to slightly adjust your thinner to paint ratios, but I have that happen with all brands depending upon the age of the paint container. Older paints tend to be thicker and need more thinner.
What thinner are you using with your paint? With enamels, I get my best results using Testors airbrush thinner, what used to come in the black can, but is now in a red can, as opposed to other types. You may even want to try experimenting with lacquer thinner for a quicker drying time.
Transferring from the tin, I use the spoon end of Tamiya stir sticks after I have thoroughly stirred the paint. X drops of paint, to Y drops of thinner from a dropper for precise mix ratios. Adjust as needed to get the viscosity that I prefer for airbrushing. Pouring from the tin just leads to messes and poor seal of the lid later on due to paint build up.
Been using Humbrol enamel for decades, main thing’s to remember is use a steel stick or the spoon as above and make sure you get ALL the paint from the bottom stirred in very well untill it’s all even and second just keep thinning until it suits your ab, don’t worry about ratio’s, it can be very thick.
I just use hardware gp or enamel thinner, Humbrol thinner is ok but more expensive of course.
I’ve been spraying Humbrols for years and didn’t have too many problems with them. One thing I had was when spraying on a hot day with too much air pressure on - then the paint landed on the model dry, resulting in a very coarse surface. Adding more thinner helped, but the real solution was to dial the pressure back a little.
As for thinning my recipe is to jugde by how it behaves in the mixing jar - the solution should leave color residue on the side of the jar, but the layer should be translucent - then it sprays right in my AB.
Some of the newer Humbrols I have bought were very thick in the can - they needed diluting to be brush painted. I have found it a little annoying, but I have thought this way I get more pigment for my buck and the paint could last longer this way (it’s the thinner that makes it decay, this is also why you shouldn’t put the diluted paint back in the can).
I have also used the Testors thinner, and now I’m using a thinner from a company called Wamod - also very good stuff.