How to keep Paint Fresh?

Hi All,

Hardly a Workshop Technique I know!

I buy 1 litre tins of oil based gloss for various jobs and would like to know if there is a trick to keeping the paint fresh once opened.

Even just opened once and a small amount used, reseal the lid tightly and turn upside down to swish the paint against the inside. As soon as I open it some time after there is a skin on the top. There is hardly any air in the tin, How come?

Is there a way around this?

Cheers, Martin

The only way that I know of to prevent this from happening is to eliminate all of the free oxygen in the pain container. This can be done by injecting a non-reactive gas that would displace the air in the container. Logical choices would be carbon dioxide, nitrogen or argon. Having said that, I freely admit that doing this requires some sort of ready-to-go apparatus (at least a small gas flask, valve and tubing), taking up a bit of space and very likely costing more than the paint it saves... not worth the time or trouble unless dealing with lots of cans of paint all the time.

Another trick I have tried (but with limited success) is to fashion a sort of floating 'lid' of aluminum foil to sit on the surface of the leftover paint in the tin. One still gets a bit of a skinning, but only at the exposed edges of the aluminum foil. To reuse the paint, slice through the foil and dip the brush. Nevertheless, given enoigh time the paint still wants to go off, albeit more slowly.

Hello Martin, I've had some success by storing the paint tins upside down. Just make sure the lids are on tightly!

David

I too store paint tins upside down and it seems to help a bit, I also tend to add a small amount of paint thinner after I have used some of the paint in the tin.

Thor

Decant into multiple smaller tins?

PITA though but maybe worthwhile if the paint is obsolete or otherwise difficult to source.

This may not work but when chefs want to prevent a skin forming on custard when making different deserts they lay a piece of cling film over the top just touching the custard would this also work for the paint as it is the paint in contact with air that causes it to skin over.

OK I'll get my coat

I often decant into clear plastic milk or juice containers (after they've been washed of course .) If you can find one or two of the right size so there is minimal air gap, and then store upside down. Bonus is you can see the colour of the paint without opening the lid. Downside is that you have to pour into another container to get a brush into it.

My dad used to add a thin layer of thinners on top of the paint, I never heard him complain about the skin problem so it must work.

Phil

Before putting the lid back on put some clean unwanted steel nuts, bolts etc to bring the level of the paint back up to the top of the tin.

It may work but you could unexpectedly run out of paint.

JA

I’ve always just put the lid on, tipped the tin over so paint can seal any 'gaps' and stored upright. If elimination of air would help then it might be simplest to stick a partially inflated toy balloon on the paint before putting lid back? Unless the paint eats through the balloon?

pgk

Edited By pgk pgk on 29/01/2022 12:14:46

I have heard of marbles, round pebbles etc being dropped into the pain to bring the level to the top to stop the skin.

no idea if it works.

Regards

Brian B

The best thing to do with paint is to use it as quickly as possible. It's like milk, glue, batteries, and condoms : they all go off, even before the packaging is opened!

Although paint dries partly by evaporation the important change is chemical. In contact with Oxygen, the binder solidifies around the pigment and sticks the whole as a hardened layer to the prepared surface. Taking the lid off starts the hardening process which continues even if the lid is replaced. Can be slowed down as described in other posts, but not stopped. It even hardens slowly in unopened tins.

For ordinary purposes old paint is often acceptable. Might not matter that it doesn't spread smoothly as before, has reduced coverage, and doesn't adhere or harden quite as well as new paint would. It passes the 'so what' test. But if results do matter, as when applying hard to reach exterior paintwork, then it's worth extending how long a paint job lasts by buying new.

Dave

Try googling "collapsible chemical container".

Regards,
Ed.

It's possible to buy small empty paint tins from ebay, I've bought large tins of machinery enamel and decanted it into 25ml tins, seems to be keeping very well and no skin on the (full) one I opened recently that's been decanted but not opened after for around four years. I make sure its very well stirred before decanting to avoid colour differences . I'm thinking of doing the same for my loco as I was not very impressed with my last tin of very expensive model paint.

I usually filter paint before use, disposable filter papers are again available online.

Dave

I don’t get this problem because I have told the wife I no longer do decorating, joking aside I avoid decorating like the plague, my back doesn’t like any decorating so it gets subbed out. In respect of models I usually use pre packaged aerosols so no skinning problem with left over paint, and nowadays the quality of aerosol paints is extremely good. Dave W

"Although paint dries partly by evaporation the important change is chemical. In contact with Oxygen, the binder solidifies around the pigment and sticks the whole as a hardened layer to the prepared surface. Taking the lid off starts the hardening process which continues even if the lid is replaced. Can be slowed down as described in other posts, but not stopped. It even hardens slowly in unopened tins."

I bought a tin of red oil paint ,made by a company named "151" in September 2020 and found that the underside of the tin was printed with "Use by May 2022." This is the first time that I've come across a "use by" date on paint; never seen it before.

Thor has the right idea.....

where I live now it's plus 30 C for most of the summer.....often up to 40......

I do as he says and it works for me......plus I have a metal cupboard thats used for storage of paint plus it's in a very dark corner of the shop where its cool'ish..........

Try freezing it.

regards Martin

I have a couple of the small Humbrol tins, which I bought when I built my Stuart 10V. Can't remember exactly when that was, but surely more than 30 years ago.Thea are stored upright, have no skin and are usable like new.
I have als some bought about a year ago, not yet sure how they will behave...

Kind regards,
Hans

I have received much help from various forum members but usually I am not able to contribute much. After a working life on the chemistry side of the paint/plastics industry it is nice to find a subject I can perhaps usefully add to.

For oil-based paint, the usual paint-makers technique is to add a volatile anti-oxidant to the paint at the last moment before canning it off. Methyl Ethyl Ketoxime is the usual one. This additive prevents skinning in the can but it must evapourate quickly from the applied paint film or it will stop the paint from drying on the job.

All well and good, but if the painter has the can open for any length of time, the anti-oxidant will evapourate out of the paint left in the can - result: the remaining paint is going to skin over in the can. The bigger the air space above the paint in the partially empty can, the more pronounced this happening will be.

There are two techniques that can be used to stop this happening:

1. Decant the paint before using it, into a number of small containers, seal them tight and use these in turn. This is the most foolproof method

2. Cover the paint left in the can with something to stop air getting to it. Any of the suggested methods using clear film etc will work fairly well but the use of a solvent layer on top will only work if the paint can will not be moved about much after adding the solvent.

It also helps to be conciencous about cleaning around the lid and can rim to ensure a good seal.

However ONE POPULAR IDEA DOES NOT WORK and that is storing the paint tin upside down. If the conditions are met for skinning are present (i.e. loss of antioxidant, too much air above the paint) then the paint will do its thing and skin. The difference is that the skin will be below the paint when the can is opened. It then becomes very difficult to remove the skin without leaving bits behind that are difficult to remove entirely.

Please note that my comments only apply to oil-based paints

Chas