I looked into books on the chemistry of surface coatings. I found
the book, Paint and Surface Coatings: Theory and Practice (2nd ed.,
Lamborne and Strives, eds., 1999) the most helpful. Most if not all
of it is free and searchable on Google Scholar. I'm not pretending
to have turned into a surface chemist overnight but here's what I
found.

Both oxidative polymerization and solvent loss are involved in paint
drying or "curing". It appears to me from my reading that oxidation
is more associated with oil-based rather than water-based paints,
though nothing I found came right out and said that real clearly.

It seems quite logical to me that an N2 or argon atmosphere will
lengthen the shelf life of paints that cure by oxidation (yes, most
of the atmosphere is N2 but O2 is a strong oxidant). The oenophile
industry has helpfully provided just the product we need (thanks for
finding that, Dennis!). I haven't decided if I'll try that but I
just might.

For that matter, if curing of water-based paints is largely due to
evaporation of the water out of the bottle, then presumably one could
greatly lengthen shelf life of aqueous paints by simply storing them
in some kind of sealed container containing water, maintaining
humidity at 100% and thus keeping the dang water in the paint
bottle. That's basically free. I think I'm going to start doing
that immediately. The only cost is convenience so even if its hokum,
little is lost.

Bob S.

--- In STMFC@..., "ed_mines" <ed_mines@...> wrote:

--- In STMFC@..., "Bob Sterner" <rwsterner@> wrote:

I could replace the atmosphere in opened paint with N2. I

believe

(though don't know for certain) that this would dramatically

improve

shelf life.

Bob, a past employer used to sell very reactive moisture cure

coatings.

We used to recommend blanketing the unused coating with nitrogen. I

did

this on many occasions, blowing the liquid out of the cans (or

bottles)

about half the time.

I don't think the coatings sold for model railroads are that

reactive

though. In fact many aren't reactive at all. (Tradional Scalecoat

is

reactive and traditional Floquil isn't.) Some reactive coatings

like

traditional Scalecoat smell for weeks; the smell is linseed oil

which

reacts with oxygen like an old fashioned paint.

Coatings in polyethylene bottles sometimes loose cosolvents through

the

plastic.

I found that traditional Floquil lasted a lot longer if the

circular

plastic seal on top of the bottle was put back intact. I many have

even

bought some replacement seals.

Ed Mines