elziko wrote:

I recently bought a solid oak table that has a care guide that states I need
to oil it occasionally but doesn't mention what sort of oil I need to use.

There are a few of relevant sorts of oil. Broadly these are "inert non
film-forming oils", "film forming oils" and "danish oils". You choose
the right group according to what you want, then choose a suitable
product from within it according to the product quality / cost /
availability.

Non-film oils soak into the wood (like most oils) and that's all they
do. This has two effects: it has an optical effect of making the wood
grain look "deeper" and generally far more attractive. Secondly they
stop other things (like water or dirt) soaking in there first. They're
not particularly robust, but then they're also easy to maintain by
continually re-applying. Kitchen woodware is an example, where the cook
(not the carpenter) happily re-oils the salad bowl a few times a year,
but knows that dishwashing it would be a bad idea.

Film-forming oils are the main sort of "finishing oil". The oil
undergoes some chemical change on the surface so that it forms a tough
outer skin. They're more resistant than non-film oils, but they're
harder to maintain. Repairing a damaged or worn finish is a refinishing
task, not just kitchen cleaning. Like the other oils, they also fill
the surface and improve the looks.

Danish oils (aka "varnish oils") are a mixture of oil and a small
proportion of varnish. They're like film-forming oils, but even more
so. They're generally tougher, but they don't soak in so well, so don't
look so good, don't enhance the grain as much and don't have as good a
surface finish.

Non-film oils are typically either mineral oil (aka medicinal liquid
paraffin from the chemist) or raw vegetable oil. Walnut oil (or many
nut oils) are good, olive oil is bad as it goes rancid. They don't
undergo deliberate chemical changes when applied. They're sometimes a
bad idea if you want to put another finish over the top later. I use
these for kitchen implements, but not much else.

Film-forming oils represent most of the finishing oils. They're usually
a modified non-edible vegetable oil. Originally linseed, most are now
tung oil. Linseed works but goes badly yellow after a few months.
They're best bought as commercial finishing oils (I use and recommend
Liberon's, but Rustins, Bollom, Briwax, Organoil and Osmo do reputable
ones too). These oils are already "dried" and "thinned". Drying is the
process of adding a chemical ingredient that enhances the oil's curing
when applied. In the past this might have involved cooking the oil for
long periods, these days it's usually a metal salt added cold. Some of
these driers have been toxic in the past, although the cured oil is
reasonably safe and certainly far safer than lead paint. The oils are
also too thick to work easily raw and so are thinned with solvents for
easier use. Don't try thinning your own oils without careful experiment
first -- sometimes there can be a reaction and the whole lot gellifies!


Varnish or danish oils are film-forming, with a varnish added to
enhance the film strength at the cost of some appearance. I use them on
tools and "rustic" work, but not on furniture. Screwfix sell a decent
cheap one that ought to be in the workshop. Some of these recipes also
lead into the "long-oil spar varnishes", which are flexible varnishes
intended for ship's rigging that will bend in service. if you want a
real varnish though, it's generally better to look at modern poly-based
formulations, not the old oil varnishes.

Nearly all oils should be considered toxic when wet, but almost all
modern commercial oils are food-safe and toy-safe once properly cured.
They'll be labelled if you want to check.

Most oils should be applied "wet" (i.e. generously) but you must remove
all the excess within 1/2 hour or you'll end up with a sticky surface
that's hard to fix.

All oils, although usually the film-formers, may produce heat on
curing. Dispose of your rags carefully afterwards or they may
spontaneously combust (lay them out flat somewhere fireproof for a
day). Linseed in summer weather really will do this!

Raw linseed is no use for anything other than cricket bats (it dries
deliberately sticky) or as an ingredient into other things. If you want
to use it, at least use a boiled linseed.


Oils are a great finish for fine furniture, but they're not as robust
against spills as some other finishes. Think carefully about using them
for table tops with drinks on.


Ikea's Skydd is an overpriced non-film mineral oil.
Ikea's Behandla is a reasonably priced film-forming oil.