Paint Bottle Hygiene
Have you ever been all ready to paint something and you open the bottle and find that it's turned to mud? I have, and it's a bummer. Not only is it a waste of paint, but now you're stuck until you can buy some more. I've read as much as I could find on what other modelers do to keep paint, and I've settled on a system that seems to be working for me.
First, I never put anything in the bottle but a clean stirrer or a clean eye dropper. I never pour thinned paint back in the bottle. Depending on the chemistry of the paint and thinner, it can cause the paint to gel. I've seen this and others have also reported seeing it. I don't even dip a brush that has thinner on it in the bottle. When I brush paint, I transfer a little paint to a dish and thin it there.
Second, I keep the threads and rim of the bottle and the threads of the cap scrupulously clean. When I remove the cap, I lay it down with the threads pointing up so that paint won't flow onto them. If the lid or bottle is messy, I clean it with some lacquer thinner on a paper towel and let it dry. This will also make the bottle easy to open the next time I use it.
Some modelers store their paints upside down on the theory that they get a better seal. I don't, but what I do is to give the bottle a quick shake after I close it. My theory is that if there is a slight gap in the seal, the paint will flow into it through capillary action and close it. Most of the paint will drain back down into the bottle by the next time I use it and the lid won't be so messy.
I don't shake the paint to mix it. I've tried the BB's or ball bearings in the bottle trick, but I don't feel like it does a good job. I've even read that some metals can react with the paint and cause it to thicken. And, if you put in something too heavy and get carried away, you might even break the bottle. It has happened.
I stir to mix. You can make or buy powered stirrers; Badger makes a nice one. I made one by putting a bent 1/8 inch diameter piece of wire in my Dremel tool. It does a nice job, but I think it's overkill. I figure that if the paint doesn't mix up well with a little hand stirring, it's probably bad and won't spray right anyway. Below is a photo of my tool of choice.
I won't guarantee that you will never have a bad bottle of paint by following my routine. All I can say is that I haven't had a problem since I began doing it. If you've come up with something better, please pass it along.
Postscript
Well, I opened a couple of bottles of Model Master enamel today, and they had gone bad. Both were about one quarter full with liquid on top and a disc of rubbery congealed paint in the bottom. The lids were on tight and the threads were clean. Both are at least a couple of years old. I checked several other bottles and they were all fine.
So, I guess I still don't have a perfect solution for storing paint. Maybe there isn't one. I store my paint in the garage where my work shop is, and last week we had temperatures of over 100 degrees F. That may have had something to do with it. At any rate, until I find a method that works better, I'll keep doing as I have been. If I do learn of anything better, I will add it here.
I got an e-mail from Timothy Welch, who says he keeps his enamel paints in a small refrigerator that he has just for this purpose. He says it makes them flow better and last longer. This makes sense since the lower temperature should slow down any evaporation or chemical reaction. Where I used to work, we stored epoxies and adhesives in small refrigerators. But, there was a strict rule that no food items were allowed in with them. So, if you have enough paints to justify the expense, it could be something to try.
Does aerosol paint go bad?
I have found that it can, but maybe not in the way you would think. I had a can of spray primer that had been on a shelf in my garage for about 15 years. I was sorting through stuff to go to the toxic waste dump, and I decided to see if it was still useable. I shook it up and pushed the button. It went spit-sput, and a little paint came out and it stopped. So, I cleaned the nozzle and tried again. Spit-sput. I even tried a known good nozzle and it did the same thing. I was determined to see if I could use it, so I tried something I read about on a forum. I threw a rag over it and punched a tiny hole in the top near the edge with a small nail. When it stopped hissing, I punched a larger hole on the opposite side. Then I poured some in an empty paint bottle and let it sit to out-gas. When it got to where I could stir it without it foaming, I tried to shoot some through my Anthem on an empty plastic bottle. It sprayed, but the finish was rough. I thinned it with a little lacquer thinner and tried again. It went on better, but still not really smooth.
Then I noticed that the paint that coated the side of the bottle looked clumpy. When I examined it closely with a magnifier, I could see that the pigment particles had stuck together to make bigger chunks; chunks that were large enough to clog the button on the can, and make a rough surface when sprayed with my airbrush. So, the can went to the dump after all.
Since then, I found a similar situation with a spray can of glossy blue paint that was only a few years old. It sprayed OK from the can, so I decanted some and tried it in my airbrush. It wasn't nearly as bad as the old primer, but I couldn't get a nice shiny finish no matter how much I thinned it. I had used it on a model when it was new, and it had gone on fine.
Post Postscript
I've done a little experiment with a vacuum pump. You can see it here.
Yet another Postscript
I had another brain storm. I wrapped Teflon pipe tape around the bottle cap. It's cheap, stretches to conform, is easy to apply, and comes off clean and easy. Maybe it will make a better seal. Time will tell.
Even more Postscript
Well, the Teflon tape didn't work. A bottle that I had it on dried up. I guess the Teflon is too permeable. But, I'm stubborn. So here's what I am trying now.
I discovered that Home Depot sells 1/16” 6”x6” rubber sheets in their plumbing department. So, I picked up a package of two sheets for about $4.50. You can tell by smell that they are real rubber. Here is what they look like. There is one red and one black.
I cut some disks to replace the original material in a couple empty ModelMaster paint jars. It's easy to cut with scissors. Then I did my lacquer thinner test. This involves putting a little lacquer thinner in the jar and sealing it. Then putting the jar inside another larger jar with a lid. Leave it sit for an hour or two and remove the lid and smell. If you can smell the thinner, then the seal on the paint jar leaked. If you can't, the seal is good. I found that if I tightened the lid down enough, the jar passed the test.
I was concerned about the chemical toughness of the rubber, so I bought a 1/16” 12”x12”sheet of Buna-N rubber from McMaster Carr. That ran me about $11 with shipping. Buna-N is supposed to be oil resistant. I cut two equal sized strips of the Buna-N and two of the rubber. Then I left one strip of each material soaking in lacquer thinner for an hour. What I found was that the Buna-N had grown about 20% in size and softened. The rubber didn't seem affected at all. So much for Buna-N.
My next experiment was to order five #3 rubber stoppers from Amazon. They were just $3.63 for all five. I found that they are a perfect fit for ModelMaster jars. I did my lacquer thinner test with one, and it passed. The only problem was that the white rubber began to crumble. Maybe quality black stoppers would work.
I still don't have a reliable fix for the problem. If I do come up with something, I will add it here.
I got an e-mail from Dave Draper. He says he blows into the bottle just before closing it. The idea is to eliminate some of the oxygen. Maybe holding your breath for a bit first would make it even more effective. Anyway, it couldn't hurt. Thanks Dave.