Enamel shelf life

I once worked in the coatings industry, and I've worked side by side with coatings chemists for the last twenty-five years.

Properly kept and cared for, paint (enamel or acrylic) can last for decades.

From your description, it sounds as if something has ruined your paint, but from the rest of your post, it is unclear whether this occured before you opened the bottle or afterwards. Once paint turns into a "goopy mass" it is generally no longer usable. This is caused by either extreme old age or mixture with incompatible materials.

Lacquer thinner is intended for use with lacquers. It may dissolve enamels, and may be useful for cleaning some of them, but generally it should be used with lacquers.

The best and safest (for the paint) solvent for thinning and cleaning enamels is mineral spirits (generic "paint thinner" is essentially mineral spirits.)

Never keep paint that has been thinned for airbrushing for more than about a week—better if only for a few days. Absolutely never return such paint to the original container.

If that is what you did with your gray paint, and you used lacquer thinner to thin (the proper paint term is "reduce") the paint for spraying, I'm not at all surprised that it turned into unusable goo.

I agree with everything said above, and I will add that the cap must be seated properly and firmly.  I'd say that 90% of the goopification that occurs with paints is usually from that.  If the cap is damaged in some way or the mating surface has paint on it then you end up with goop in the bottle.  When I thin paints, I usually use the manufacturer's recommended agent.  That is unless I am positive about a substitute.

Ivan, the shelf life of your paint starts with what it looks like when you buy it off your dealers rack. Carefully roll the paint bottle around, do you see a big glob of goo? Or is it fairly smooth where a few shakes and it's ready for painting with? Goo, leave it as it's already too old. Many distributors require that the dealers by the paint by either a 6-pack or 12-pack of each color. So it's not uncommon for paint to sit on a shelf for ages.

If the paint sits for awhile and gets a bit thick and needs stirring, that's normal as long as it's no thicker than, oh say, toothpaste... well actually a bit thinner. I have some enamels that been kicking around for years.

Lacquer is enamels enemy, they don't mix.

Years ago I read a artical that if you want to store your paint drip hot wax around the lid of a closed bottle. and it will give you a good seal. J

urich wrote:

Years ago I read a artical that if you want to store your paint drip hot wax around the lid of a closed bottle. and it will give you a good seal. J

Something similar but easier that I've always done, was to have a wet coat of paint (thin) around the lip of the jar before screwing the lid back on. Mostly for the colors I don't use often. I might need pliers to help open the jar, but it forms a tight seal. Just be careful of any paint chunkies if painting straight from the bottle.

Or better and easier, store the bottle upside down.

jhande wrote:

urich wrote: Years ago I read a artical that if you want to store your paint drip hot wax around the lid of a closed bottle. and it will give you a good seal. J Something similar but easier that I've always done, was to have a wet coat of paint (thin) around the lip of the jar before screwing the lid back on. Mostly for the colors I don't use often. I might need pliers to help open the jar, but it forms a tight seal. Just be careful of any paint chunkies if painting straight from the bottle.

I have to disagree strongly on this one, Jim, partially for the reason you've stated, and partially because this makes it almost impossible to get a good seal the next time you close the bottle. Paint is a good sealant on flat surfaces, but it doesn't do corners—that's what caulk is for.

The wax idea has some merit, but it's messy and overkill. I think it would be just as effcetive to rub a little wax on the rim of the bottle. Use parafin for aqueous systems, and beeswax for organic solvent systems.

jhande wrote:

Or better and easier, store the bottle upside down.

Absolutely! I had forgotten this (getting senile, I guess). Jim, may I credit you with this in the article I'm writing?

I've got several bottles of Pactra and Testors and some tins of Humbrol that date from the late 60s and early 70s that are very usuable.  Some are everyday colors that are still availble from one mfgr or another to this day.  Others (Pactra's Hot Rod Primer or Humbrol's Doped Linen come to mind) are no longer produced and only get used for special models. 

When I get done using my "special" colors, I wipe the lids and neck areas clean with a thinner soaked rag before closing the container.  In addition, the glass bottles get the top covered with Saran Wrap before the top is screwed on.