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Discussion Starter #1
I recently bought some tung oil (Formbys) and some Danish oil (Watco) in 1 quart cans. I put some of each in 1/2 cup glass containers for convenience. The Danish oil is like new but the tung oil in the glass container has turned to wax. Also, I use Minwax Polyurethane, and have to buy a new can about every four months. It gets so thick it can't be applied. After five or six months it turns so solid I can't push a screwdriver into it. Whatsup?
 

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Some finishes start to react with the small amount of oxygen in the air once the container has been opened.

You may get slightly longer life if you purge the container with Bloxygen or some other chemical. I use CRC Duster. A lot cheaper than Bloxygen. I do not get as much skin on the poly when I purge the can. It will eventually go off though.
 

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Oil based finishes have just about an indefinite life, until the can is opened. That allows the start of the curing process and it won't be long until it's, well, cured. That's waht you are seeing. You can do things like Dave suggested (and a few others) to slow it down, but it's best not to expect it to last too long once opened. Keeping it in a refrigerator also helps. For what seems to work best is to either 1: cover the finish with a piece of wax paper cut to fit inside the can, or 2: fill the finish can with something (marbles) until it's full enough to push almost all the air out.
 

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Discussion Starter #5
Perhaps

I can transfer all the finishes to 1/2 pint mason jars and vacuum seal them?
 

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I've tried vacuum sealing (believe it or not) a couple of ways. The first, I actually cut the port out of one of those Ziplock vacuum bags, and put it on a paint can lid for a can of varnish. I had perforated the lid right under the port to draw a vacuum. Really worked (the vacuum part) since I could crush the can pumping the air out. But it didn't seem to help. Next I tried just using a gallon size Ziplock, put the quart can in there, and then suck it down. That didn't seem to help either. I'd like for someone else to try it and see what happens. Maybe my method needed to be tweaked. Anyway, the pint jars should help, if the finish fills them up.
 

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Discussion Starter #7
Here's what I did

A few days ago I got out my 1/2 pint wide mouth jars and the vacuum unit. The 1/2 pint jars won't work with the vacuum, so I put 1/2 pint of tung oil in a 1 pint jar, drew a good vacuum on it and set it away for a while. Then filled a 1/2 pint jar as full as I could get it and purged it as best I could with ........propane. All has been set aside for a while to see what happens. With my next can of poly I'll try to get something to float on the surface to help reduce the O2 level. I might be able to get a small bottle of nitrogen to purge this stuff with.
 

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Every different finish is going to have a different shelf life. I've had lacquers that dried up in the can to a paste and put thinner in it brought it back to usable condition. You can often prolong the shelf life by putting something like marbles in the paint can so the finish comes to the top like when it was first opened. The less air in the can the better. You can also buy empty paint cans at most paint stores so if you have a quart of paint left over it's better to transfer it to a quart can. Temperature plays into it also. If you keep paint in a cool place it will last longer too. Yesterday I was at a customers house and they wanted me to repaint the woodwork in their house the same color and I asked them if they had the paint they used or the color formula. They took me to the basement and got a full gallon of paint the label had rotted off which they painted the woodwork 28 years ago. I opened the can and the enamel paint was still usable with the exception some rust from the can had gotten in the paint. I was able to strain the paint enough I could make a sample to get some fresh paint.
 

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Removal of oxygen will accelerate the curing process. The oxygen will quench the free-radical polymerization which is the source of increased viscosity and thickening. The first step in any polymerization (making polyethylene, for example) The radical inhibitors I have worked with are not commonly available and are typically used at ppm levels. While I haven't worked specifically with preserving oil finishes, my first try would be to add a small amount toluene (also sold as 'toluol').

Regards,
Steve
 
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