Paint, as understood by oil painters and artists, sounds like a slightly different animal than paint as understood by house painters, wood finishers, and other sorts of people with more prosaic requirements of their paints.
Bob Flexner wrote a book for wood finishers, Understanding Wood Finishing, that breaks down oil paint in simple terms for the rest of us:
Some oils (like linseed and walnut) are drying oils, and can be used as a finish on their own, but don't really form a hard film finish.
For that you need a varnish, which is an oil cooked with a resin.
Paint is a varnish with a pigment added.
That's different from an oil mixed with a pigment mentioned in the article, which is probably fundamentally similar to a straight oil in terms of its properties. Maybe somebody who paints with oil paints can weigh in?
His columns in Popular Woodworking and other woodworking magazines are worth a read, as is his book, if you're interested in understanding what you're really working with.
Tying this all back to the article, I'd disagree with the claim that paint is "colored glue". One typically doesn't glue things together with paint, though that is a sometimes unintended consequence of putting something on top of something else with an incompletely cured layer of finish. You certainly couldn't use e.g. linseed oil as a glue in a joint where oxygen isn't getting in readily like a mortise and tenon joint.
basic linseed oil takes ~70 years to cure properly. pure linseed does, in time, a nice hard firm.
there are a number of plant oils for painting (saffron, sunflower, walnut, linseed, poppy: different dry rates and hardness rates), and there are a number of ways for treating them. Specifically we usually avoid plain boiled linseed oil, as it tends to yellow. That is, I believe, the common hardware store oil paint.
fundamentally - artist oils are engineered for divergent purposes than house oils.
resins are hugely variant - artists are usually suspicious of things that aren't engineered & tested to last > 50 years, so house painting probably has a much larger variety.
the pigments affect the oil dramatically. quinacridone pigments stay wet for days, if not weeks, whereas umbers (due to the manganese) will dry within 24 hours.
with respect to varnishes, that's not how oil painting artists think of varnishes: a traditional varnish is dammar resin dissolved into (pure) gum spirits of turpentine, laid on about 6 months after the painting is touch-dry. Today we typically use a acrylic varnish with a UV protectant, i.e, what's sold under the trade name "Gamvar". Such modern varnishes are designed to not link against the oil and permit stripping and reapplying to use as a protective layer.
it's technically correct to call oil paint colored glue, I think. But it's not useful to think of it that way. I think of it as "oily mud applied with a hairy stick" when I feel reductionist.
I love talking about artist oil paints, happy to answer any other questions.
Not a direct response, but in the case of modern automotive paints, especially 2 part urethane or epoxy ones it is exactly right - they're even based on the same chemicals!
Of course, that doesn't really mean that paints work as glues, but you can add pigment/dye to a lot of glues and get a workable paint. (workable in the sense that they will adhere and color. they may not have the consistency that makes them work well as a paint).
> One typically doesn't glue things together with paint
A friend of mine had his house repainted and the contractor farmed it out to some idiots. They painted all of the windows shut. No one noticed until after the paint had dried.
It's as solid a glue as you could want. :-)
(As anyone who's been sloppy and lazy with a can of paint knows.)
From what I know about wood finishers/lacquerers, their requirements seem anything but prosaic, there's a whole science behind it - especially for those in business of refurbishing old/antique furniture.
I would guess that the main reason for linseed oil not forming a hard surface coating on wood is that it doesn't form a surface coating at all. It soaks in.
Maybe if you saturate the wood, let it dry, and then keep adding additional coats, you'd start to get one. But, in a world where varnish exists, I'm not sure why you'd do that unless you were trying to reproduce a period technique or something.
There are many different types of bases ("resins") many of which are incompatible which each other, and can neither be mixed nor painted over. E.g. even acrylic lacquers, you can make them as a dispersion (i.e. water based) or using a solvent. Different paints. Not compatible. Both are "acrylic".
Bob Flexner wrote a book for wood finishers, Understanding Wood Finishing, that breaks down oil paint in simple terms for the rest of us:
Some oils (like linseed and walnut) are drying oils, and can be used as a finish on their own, but don't really form a hard film finish.
For that you need a varnish, which is an oil cooked with a resin.
Paint is a varnish with a pigment added.
That's different from an oil mixed with a pigment mentioned in the article, which is probably fundamentally similar to a straight oil in terms of its properties. Maybe somebody who paints with oil paints can weigh in?
His columns in Popular Woodworking and other woodworking magazines are worth a read, as is his book, if you're interested in understanding what you're really working with.
Tying this all back to the article, I'd disagree with the claim that paint is "colored glue". One typically doesn't glue things together with paint, though that is a sometimes unintended consequence of putting something on top of something else with an incompletely cured layer of finish. You certainly couldn't use e.g. linseed oil as a glue in a joint where oxygen isn't getting in readily like a mortise and tenon joint.
A discussion of oil vs varnish here:
https://www.popularwoodworking.com/techniques/finishing/oil-...