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View Full Version : Why do metal tubes work so well at keeping paint fresh?


Richard P
04-16-2019, 04:56 PM
I've read a lot of threads on here (and other places) about ways to keep pre-mixed paint fresh. Freezers, clove oil, foil, saran wrap, syringes, ice cube trays, water, etc..

Yet it seems that even when covered in wrap or foil or exposed to very little air, the paints still don't last very long.

Why then are metal tubes so good at keeping paint fresh for years? I would have thought they'd still be a bit of air in there, or are they really that tight around the paint (even with a nearly empty tube)?

WFMartin
04-16-2019, 07:18 PM
I've read a lot of threads on here (and other places) about ways to keep pre-mixed paint fresh. Freezers, clove oil, foil, saran wrap, syringes, ice cube trays, water, etc..

Yet it seems that even when covered in wrap or foil or exposed to very little air, the paints still don't last very long.

Why then are metal tubes so good at keeping paint fresh for years? I would have thought they'd still be a bit of air in there, or are they really that tight around the paint (even with a nearly empty tube)?

The probable reason is that when a metal tube is squeezed, and pressed flat, it does not have a tendency to "pop back" to its original form, as some plastic tubes tend to do.

Whenever a tube regains is original shape after it has been squeezed, it is an invitation for air to take the place of the previous paint.

There is really very little "air" that contaminates the paint remaining in metal tubes, either before, or after they are squeezed. By their very nature, some paints tend to polymerize because of their specific ingredients, and the introduction of air has very little to do with such hardening of paint in the tube. There is not much you can do to prevent such a hardening in the tube of these paints.

Anyway, "no air" is the general reason that metal tubes keep paint fresh as well as they do.

sidbledsoe
04-16-2019, 08:02 PM
they are non permeable to air and seal up nicely with the small threaded cap.
they seal much better than a wrap of foil, but if you get one small stress crack opening, the paint inside will begin hardening. I tape those with duct tape which seems to work ok.

my plastic tubes of Permalba white tubes do not spring back, they remain absolutely flat as they are dispensed.

since some plastics are semi permeable to air exchange, these tubes also have an inner lining of metal foil, I dissected one one time and did verify that there was indeed a metal foil layer.

this foil layer lining is a common practice with plastic tubed materials that are air sensitive such as, medicines, and cosmetics, too.

ronsu18
04-17-2019, 07:28 AM
an aside to the basic problem; the brand of paint matters, since most brands manufacture paints to be combatible within series, drying-wise. i've kept a paper palette with mussini out on the porch for weeks, temp +10C to -10C. the series is somewhat regulated with siccative, fast drying, and the only loss was burnt umber.. it only lasted let's say three days.

if still inclined to test, find an ice cube tray with lid; posit paint in then fill with water covering the paint, close with lid; into the fridge.

Pinguino
04-17-2019, 12:58 PM
Slightly related to the original topic, slightly not: As already noted, some plastics are more permeable to oxygen than are others.

Polyethylene and related "soft" plastics tend to be somewhat permeable. This is the kind of plastic often used in squeeze bottles of shampoo. So, if you ever think of long-term storing linseed oil is a rinsed-out former bottle of shampoo, that's a bad idea. Likewise oil paints. However, this material is less permeable to water vapor, so it might be used for acrylics.

Saran Wrap® is in the above category, as are most plastic ice cube trays. The purpose of the plastic wrap is to reduce moisture loss, and to prevent food odors (heavier molecules) from escaping, rather than to prevent air from getting to the food. The ice cube trays are flexible, to help dislodge the cubes, so the plastic is not very dense.

Water is partially permeable to oxygen. It's how fish breathe.

Plastics that are less permeable to oxygen tend to feel "crinkly," even when very thing. This is the kind of plastic used for bags of potato chips, and other products that would lose flavor if exposed to air for a long time. In fact, some of these fast-food products are fried in sunflower, safflower, or cottonseed oil, and need to be kept free of oxygen so that the oil doesn't cure. I suppose you might try to clean and save your bags of Cheetos® for future paint use, but I doubt if that would be most effective, as well as been a hazard to those of indiscriminate taste.

Aluminium foil ought to be a good barrier, but it may be the case that the foil has sufficiently many natural pinholes that it is somewhat permeable. After all, the purpose of the foil is not to seal from air.

Richard P
04-17-2019, 03:45 PM
Thank you all, very interesting and insightful!

So I guess we are looking at tubing mixes, or some kind of PET container, perhaps with a foil barrier? Mylar bags?

Raffless
04-17-2019, 05:12 PM
Original tubes were longer and thinner. They lasted longer. So modern manufacturers shortened and widened the tube so the paints dont last as long due to increased surface area inside the tube, making you buy more. Just a small point taken with a pinch of salt 🙀

sidbledsoe
04-18-2019, 01:58 PM
Original tubes were longer and thinner. They lasted longer. So modern manufacturers shortened and widened the tube so the paints dont last as long due to increased surface area inside the tube, making you buy more. Just a small point taken with a pinch of salt 🙀
what does the surface area inside a tube matter if the tube is non permeable to air?
why don't large Wintons just dry up right there in their honking humomgous tubes with all that surface area?
When were tubes longer and thinner, back in 1920?
How do you know that they lasted longer back then?
data?
need a lot more than a pinch of salt for this one :lol:

french.painter
04-18-2019, 05:24 PM
Also because tubed oil paints are not very siccative. Ground with soy-bean or poppy oil.
When I mull my own oil paints, they don't have such long shelf-life, even when tubed without any air bubble in them.

Raffless
04-18-2019, 07:14 PM
what does the surface area inside a tube matter if the tube is non permeable to air?
why don't large Wintons just dry up right there in their honking humomgous tubes with all that surface area?
When were tubes longer and thinner, back in 1920?
How do you know that they lasted longer back then?
data?
need a lot more than a pinch of salt for this one :lol:

There is no data. There is nothing written about it. Its just the conspiracy theorist in me. But the less surface area of a thinner tube(top) would suggest less oxidation in that part of the shaft 😖

sidbledsoe
04-18-2019, 09:27 PM
Ok but paint maker/sellers would also have to be incredibly foolish to want their paints to dry up hard, right in their own darn tubes!
what a selling point, who wants to keep buying more and more paint
that rapidly turns to concrete? that should kill their business but good :crying:

Ted Bunker
04-21-2019, 12:37 PM
Before aluminum became cheap, some early paint tubes were actually lead foil. Tin Foil was still used in cigarette packs until recently since tabacco and aluminum foil reacted. While cast zinc is brittle, they also used zinc foils for packaging. I think the old toothpaste tubes that came with a winding-key were zinc foil.

I have some unopened W&N oil paints in metal tubes of my mother's that are still "squishy" that must be atleast 30 years old.