What makes varnish

[SandMaster]

Turn into that tranluscent gooey useless mess in the can?

[Pernicious Atavist]

air.

okay, that's obvious, but every time you open the can, vaporized solvents escape and new, unadulterated air is introduced. this air then absorbs the solvents that keep the varnish liquid, and the process is repeated the next time you open the can.

[pipefitter]

If you could put it in a plastic container and squeeze it until the liquid reaches the very top,close the lid with it in it's squozen state minus the air space,it would last a very long time.That's the treatment I give the bottle of tung oil when i am through with it.Stays good for years.
Also,carbonated soft drinks will not get flat nearly as fast stored in this way.

[ 09-05-2005, 11:28 PM: Message edited by: pipefitter ]

[Dan McCosh]

"Drying" varnish actually is partially a chemical process that changes the consistancy, as well as simply letting the violatile portions evaporate. The chemistry can be activated by the presence of air, oxygen, etc., as well as reducing the solvents. The gooey mess is the result.

[ 09-06-2005, 08:49 AM: Message edited by: Dan McCosh ]

[ssor]

One method that has been used to prevent the skinning in paint and varnish is to purge the air from the can with dry nitrogen. Varnish dries by oxidation, this is why they add driers to the mix. Laquer on the other hand dries by evaporation of the solvents.

[Pernicious Atavist]

an old painter showed me a way of excluding air from the container by adding marbles to it until the surface of the paint--varnish in this case--reaches the lip. this prevents that big air space left when you use the product. introducing n is a good idea, so is the plastic container. of course, you don't have the fun of collecting all them maw smile.gif bles!

[SandMaster]

This may sound strange but what would be wrong with a zip lock bag?

[Keith Wilson]

Varnish doesn't dry by evaporation, but by reaction of the drying oils with oxygen (although there are solvents that evaporate as well). Shellac, for example, dries by evaporation only. Anything that keeps oxygen away will work; the ziplock bag idea actually isn't as odd as it sounds, athough there are some obvious practical difficulties. ;)

[Scott Rosen]

Originally posted by SandMaster:
This may sound strange but what would be wrong with a zip lock bag?The solvents in the varnish would dissolve the bag.

[WoodenBNut]

Heh Pipefitter,
That is a great idea about using "squeezable" plastic bottles (with sealable caps) to store varnish! Just squeeze than until the varnish fills the entire container (no air/oxygen) and put the cap on. Simple and I would think a very acceptable solution. I think you just have to make sure that you use high density polyethlene plastic bottles/containers so that the varnish doesn't dissolve the container. Heh, I am going to put this idea to good use.
Thanks

[JormaS]

The squeezable bottle sounds like the perfect way. I have so far used wine bottles with the vented plug/stopper, pumping out the air from the bottle with the appropriate hand pump. Very little oxygen remains in the bottle; the varnish seems to stay fresh forever. But the plastic bottle seems more simple. I´ll try that. smile.gif

[pipefitter]

I recently bought some of those disposeable ziplock tubs for paint cups. I have had some paint in one (brightsides) for about 3 weeks and it hasn't softened the container. I had only intended to use them for a couple hrs but I had some paint left over with the thinner in it that I didnt want to add back to the can and it is still intact. I felt that the containers with the lids would temporarily help the paint from losing it's solvents while I was using it in this heat keeping the mix more consistent throughout the day.Plus I hate cleaning out the groove in the metal cans every time I pour paint. The tung oil is in a white colored plastic bottle and I collapsed all the air out when I last used it 7 years ago. I just went and looked at it and it is still thin like when I got it. I am not sure if tung oil stands up better over time in storage like that than varnish does but it seemed to dry pretty fast in use.

[dmede]

Here's a related question:

Does the fact that some of the varnish has dried in the can change the make up of whats left such that it can not, or should not, be used?

I know a little drying is not a problem, but what about when you get a good skin over the top and pull it away to strain and use the remainder? If this happens several times, is whats left of the varniish still in proportion to its original, less the volume lost or is some change occuring that effects the ratios of ingredients that might be important?

Dave

[JormaS]

My bet would be that it does´nt change the remaining varnish at all. The oils are drying on the surface in a normal way, using up the oxygen which is available in the can. That´s all, as far as I know.

[JimConlin]

After more than one de-skinning, i'll only use the varnish for setting bungs.
Another suggestion for smaller containers for remnants of varnish- Use smaller paint cans. Good paint shops sell empty cans.

Aside from the question of what solvents will soften what plastics, Most plastics are far from vapor-tight, so the solvents will gradually escape, leaving goo.

To minimize this problem, i buy varnish only by the pint.

[Matt Cohen]

Suggestion from the guys at Epifanes on how to best close your can to avoid this problem in the future.

Take a piece of plywood, place it over the semi-closed lid of the can, and firmly press down with your upper body weight. This seals the can, prevents dents that lead to air-leakage, and avoids shaking the can, which leads to fish-eyes.

[AlanWS]

Here's the perspective from a chemist. Sorry about the length.

Let's stick to traditional varnishes that consist of a resin in a drying oil, with some solvent. When the varnish dries, several things happen: the solvent evapoates, leaving behind the varnish, and the drying oil cures.

This curing is chemically pretty complicated, and depends initially on reaction with air to form peroxides that are similar to the stuff you add to a polyester resin to make it harden. The "dryers" added to oils to make then "boiled" help with this step.

Once the peroxides are present, the varnish will cure. The cure is faster at higher temperature and with more peroxides. If it cures in the can, the solvent is still present, and you can get a gel, rather than a hard film. Oxygen at this stage can have various effects: it directly slows cure, but it forms more peroxides that speed cure.

If you want to keep your varnish around for a long time without curing, the thing to do is to open it briefly, pour the amount you will use into another container, flush the air out of the original can and seal it up right away. You don't need to be careful with the stuff you poured out -- just use it. But don't pour it back into the larger contained if you have any left at the end, or it will cause the whole can to slowly harden.

How do you flush the air out of the can? The thing to remember is that you are not trying to put something into the can but to flush out something -- the air. So if you use bloxygen, put the cap on loosely, stick the tube under the edge, and run it for a bit, then immediately pull the fill tube out of the way and seal the can without opening it. You want to add much more than the volume of the can to be confident of flushing out most of the air.

The cans sold for blowing dust off of electrical devices are much cheaper than bloxygen, and equivalent. A CO2 fire extinguisher would also work fine, as long as you could keep the flow down enouogh that it didn't spray the varnish all over the room.

Some plastic containers might work, but the problem is that oxygen, the culprit in varnish cure, can pass through some plastics that keep water out. The plastic bottles used to contain refrigerated food don't need to hold out air for long. Ones designed for carbonated soda and beer may protect better against oxygen, but might be more easily attacked by the solvent in the varnish.

[pipefitter]

7 years is a pretty good indication that the correct plastic was used by the tung oil manufacturer.
I was just surprized that the ziplock containers actually held up to the solvents of the paint.I put it in there with the lid on it so as not to have to guess how much solvent I was losing or thinking that I was thus messing up an already perfect ratio that was working for me. Whether it did anything or not is beyond me but it didn't hurt since the lids came with the containers.Plus I didnt end up having Murphy to lead me to spill it or kick dirt in it. smile.gif