Salvaging old jars of enamel paint

[Cool Hand]

Hi guys,

I'm need some advice on saving a jar of paint. The pigment has settled into a spongey mass on the bottom fo the jar.

It's Model Master flat gull gray enamel.

Thanks and cheers

-Chris

[Triarius]

If it's spongy, it's history. The binder has started to cure.

[Cool Hand]

Thanks guys.

I figured that was the case.

Cheers :)

-Chris

[mossieramm]

Unless the paint is dried up and crusty, you should be able to restore the paint by adding some laquer thinner.

David.

[Triarius]

Unless the paint is dried up and crusty, you should be able to restore the paint by adding some laquer thinner. David.

Sorry, but that turns out not to be the case. Once the paint has started to cure, even slightly, it cannot be made useable again. If it is rubbery or spongy, if there are strings and moderately cohesive blobs (that become strings when you try to disperse them) it has started to cure. You may be able to make it look useable again, but it won't produce the same quality of finish, at best, and will gum up your airbrush, at worst.

[Mark M.]

MM airbrush thinner will congeal a bottle overnight in some cases. There's a chemical reaction at work. If even a minute amount on a paintbrush gets into it, kiss the jar goodbye. I've had full, new, jars, harden overnight because I had a bit of thinner on my brush, and dipped it back in. It does something funky.

Same for acryl thinner and acrylics.

[mossieramm]

Sorry, but that turns out not to be the case. Once the paint has started to cure, even slightly, it cannot be made useable again. If it is rubbery or spongy, if there are strings and moderately cohesive blobs (that become strings when you try to disperse them) it has started to cure. You may be able to make it look useable again, but it won't produce the same quality of finish, at best, and will gum up your airbrush, at worst.

We'll have to agree to disagree. It all depends on how far the paint has dried up. If it is like really thick paint, no dried bits, the paint should be usable again, specially if you are brush painting, although airbrushing works fine as well.

David.

[Triarius]

We'll have to agree to disagree. It all depends on how far the paint has dried up. If it is like really thick paint, no dried bits, the paint should be usable again, specially if you are brush painting, although airbrushing works fine as well. David.

No disagreement that I can see—paint that has merely lost solvent and thickened is entirely salvageable. It can be hard to tell, especially if the cure has not progressed very far, whether a paint has merely thickened or has actually started to cure. Being a former coatings technologist, I know this from experience :) . :(

As paint dries, it thickens, allowing the short polymer chains of the binder to come into closer and closer contact. When they get close enough, polymerization begins—and it's a one way process with enamels and acrylics.

For most paints, if it can be redispersed completely, with no lumps or strings, to a completely liquid state—regardless of how thick—by hand stirring alone, before any thinning, then thinning will return it to its original state. If there are any solids or semisolids after about five to ten minutes of stirring, then it is best to get new paint.

[TheRealMrEd]

Unless the paint is dried up and crusty, you should be able to restore the paint by adding some laquer thinner.

David.

Generally, I agree, except that all cases I've ever had of MM paint going bad was when it had been thinned or exposed (by dipping a brush cleaned) with generic laquer thinner. I now thin MM and Humbrol paints with MM thinner and none have gone bad in years.

FYI I have been able to recover 20+ year old MM enamels and 30+ year old Humbrol enamels, that were VERY thick, by stirring by hand as much as posible, then adding a couple BB's and some MM thinner and setting the resealed container on my Robart paint mixing for 15 minutes or so. Come back, stir some more, add more thinner, another 15 minutes on the Robart, etc, etc, and voila, good paint again.

As you can tell I am old and very cheap!