An understanding finally crystallized for me this morning. Last week I went to two different hobby shops to buy paint. I picked up some Humbrol acrylic and shook it and nothing moved. I opened it and found it was completely dried out. I tried two other bottles and found the same thing. I went over to the Vallejo rack and found multiple bottles of Vallejo paint also dried out. These had never been opened. Today it dawned on me that it’s not only the age of the paint that matters but the container it sits in. Plastic breathes. These paints in plastic containers are drying out because they are in the plastic bottles. Long after paints in plastic bottles dry up, Tamiya, Model Master, and Testors paints will still be ready to use.
You make a lot of sense with this interesting observation. I looked at my paint supply and beheld that all my paints are in glass jars…lucky I think since I didn’t actually plan to buy glass jars exclusively. Needles to say , I have had no drying out problems.
I have Vallejo paints that are 10-15 years old and still work fine, even after having been used. Thre is clearly something other than plastic bottles to account for your observations.
That’s very helpful and encouraging since I have dozens of Vallejo paints. I know the paints had been sitting in those racks for years because I asked the owner about them. Now, I am wondering what’s going on. I know rubber breathes. Tires lose air for that reason. That’s why some people put nitrogen in their tires. Apparently, the larger nitrogen molecules don’t pass through the rubber. That’s what made me think the same thing is going on with plastic paint containers. I’m happy to have others weigh in. This could really affect my paint buying decisions. There’s no sense in stocking up on colors I might need some time in the future if it is just going to dry out in a few years.
I’ve bought my fair share of Model Master (both acrylics & enamels), and Gunze/Mr. Color acrylics from my LHS only to find them really gummy. None are in plastic bottles but glass bottles. Now I open and check the quality of paint before buying.
Had been using craft acrylics from places like Jo-Ann fabrics and A.C.Moore that come in plastic bottles and have had no trouble with them drying out. I am using Vallejo acrylics for the past few years now along with the craft acrylics and am not having any drying out problems with either.
If the bottles are truly the problem, I am wondering if the humidity in your house has something to do with it. Very low humidity would tend to draw the moisture out of the bottles. My house runs in the 50 to 60% range. Maybe someone with more knowledge of that kind of situation could help figure it out. [2cnts]
Jim [cptn]
I have had some (just a few) of my Model Master paints, in glass jars, dry out after a few years. But, I also have many, many of them that are still good after 15+ years sitting awaiting another use (I have used all of them at least once since I’ve bought them). I have a little over 100 jars right now. I question the plastic breathing issue, as many things use plastic as a sealer. Zip-Lock bags come to mind…
Devil Dawg, I wondered the same thing, so I did some checking. It turns out that Ziploc bags are gas permeable. It just takes a long time for any appreciable amount of gas to work its way through the plastic film. The thicker the plastic, the less gas permeable. So, for example, plastic freezer bags are thicker than sandwich bags and are less gas permeable. I’m still thinking these plastic containers are less dependable than glass ones for this very reason. Clearly, we’re talking years here, but I have some Vallejo paints going on years now, and never used yet. I’ll be irritated if I do finally go to use it and find it dried up. I’m also wondering if the problem might be in how tightly the caps seal. They might not be able to get as tight of a seal with soft plastic bottles and caps compared to glass and steel (Model Master) or hard plastic (Tamiya). Fortunately, we’re not talking a loss of a lot of dollars, mostly just aggravation.
I have Humbrol tins and Testors paints 30+ years old and are still good. Then I have Testors paints just recently purchased to go bad on me. I think it has to do more with the poor quality of the product(S) as compared to years back.
Now, they charge you more, they give you less and goes bad faster. 
The type of seal at the lid plays a part too. If you have an old Testors bottle where the gasket at the top has become torn up or encrusted in paint it will dry out faster no matter how tight you screw on the lid.
^^^^^^^ This.
+1
I’ve had Vallejo paints I’ve been using for ten years or more but had paint in glass bottles go bad in less than a year. CN Spots I think nailed it, if the lid isn’t perfectly airtight it paint will dry out and go bad. Sometimes it seems to take only a smidgen of paint on the rim to ruin the seal.
PS: People put pure nitrogen in their tires??? Um, regular air is about 78% nitrogen already!
As a matter of fact we use pure nitrogen in the tires on the sprint cars we run. Nitrogen isn’t affected as much as regular air when subjected to the heating of the tires on asphalt. With regular air, for example, we’ve put 10 psi in the right rear tire before taking the track, come back in after a few laps and the pressure is up to 15 to 18 psi and the tire has shrank. Compare this to nitrogen, same pressure and the tire may expand slightly but the pressure may only increase a a pound or so.
Sorry for hijacking the thread, just giving some examples.
As some one pointed out, it is not actually a metal to glass seal on Testors/ModelMaster jars - the piece of cardboard in the lid is the seal. Take that out, and see what happens to your paint. I’m highly dubious of this ‘theory’ of the plastic jars being ‘permeable’, too. There’s no mystery; the plastic to plastic seal is not that good. Or not capped very tightly.
In fact, you can go to your local store if you have a Vallejo rack, and probably find a fair number of the caps are loose right on the rack, and that you are able to tighten them up a fair bit. Games Workshop paints are notorious for drying out since they changed from the ‘bolter shell’ bottles to their current design. But again, it’s not the plastic. The pot’s design frequently prevents a good seal from forming if there is a paint buildup on it, particularly near the cap hinge. You may think you’ve snapped it closed…some have gone so far as to accuse GW of intentionally designing it this way…
Thanks! The day is never wasted when I learn something new!
Actually, once used, the tightness of a Vallejo style cap becomes less of an issue since a small amount of paint will dry and seal the opening. The other thing about the opening is that it is much smaller that any traditional paint openings allowing less surface to be exposed to air and to dry up.
I do have to comment here .;
I have some Testors M.M. paints that are going on about fifteen years now . Some have been opened and used some have not . I also have some Vallejo that way . Guess what ? they all separated and all that , but were ready to use again after stirring , Not shaking and here’s something I do faithfully .
I always clean the inside of the tops till they are clean , as well as the tops of the bottles , whether they look like they need it or not . I’ve kept mixes good that way for years . Also , I keep all my paints in a cool , dark place . I/E the bottom of a file cabinet set . that’s if they are bulk buys , which I do often .
One more thing though . I NEVER put any paint in the Plastic jars you get at Hobby Lobby . I have had them soften even with Vallejo mixes . I buy the Glass ones offered in Squadron and Micro-Mark catalogues . If I am desperate , I use old paint bottles after cleaning them out with Lacquer thinner and a good soap and water , wash and dry .
It may be tedious but a cotton goes a long way.
Cotton swab
tankerbuilder -
A thought came to me concerning your comment regarding plastic bottles particularly; Vallejo brand. I often wondered if transferring Vallejo paint from their own plastic bottles to glass jars would be a good idea to improve shelf life and easier stirring prior to using. Thoughts?