Will this layered finish work?

[GarF]

The finish I've planned for a few small items I'm making at the moment is danish oil followed by garnet shellac to add some warmth, then buff up with carnauba wax. I'm happy with the tests I've done on scraps, just wondering whether I'm going to run into any obvious problems as I've never attempted a multi step finish before. I'm assuming the oil should be sufficiently dry to apply the shellac after sitting overnight in the warm air from my dehumidifier (in otherwise unheated garage).
G

 

[Rich C]

Why oil and shellac? I'd be tempted to just go for shellac alone.

 

[CHJ]

'Danish Oil' can be a variable blend of oils depending upon the manufacturer, all will be a polymerising oil blend though with 'driers' to speed up the curing that relies on crosslinking with the oxygen in the atmosphere to form a 'cured' surface, so technically do not dry as they don't rely on solvents or water to evaporate.
I would expect the timescale to form a robust surface suitable to stand up to buffing with a higher temp wax such as Carnauba to possibly be days rather than hours.


I personally would not put a spirit based Shellac on top of an oiled finish on the basis I would not be surprised if it ended up showing as a reticulated finish at some time in the future.

For small items that do not need to stand up to heavy abuse I would just Shellac.

 

[profchris]

A good rule of thumb is Fat Over Lean, never the other way around.

An oil finish over a shellac base works nicely, and is not uncommon for finishing musical instruments. All the luthiers I know would advise not to use the oil finish as a base, for two reasons:

1. Oil finishes takes weeks to cure, probably months to cure fully. Shellac on top will slow down that curing a lot.

2. Oil is soft, shellac is hard, when cured. So something like a fingernail press will crack the shellac film as the oil below deforms. And the oil finish will shrink as it cures, pulling the more brittle shellac into a lovely craquelure effect!

 

[Sgian Dubh]

... danish oil followed by garnet shellac to add some warmth ...

Shellac is well known as an all round barrier coat or sealer between problematic surfaces and subsequent finishes. The rider is that the shellac needs to be a dewaxed version in order to be sure other finishes such as oil based varnish, various lacquers, and so on will adhere to the shellac.

So, for example, if you suspect contamination on the surface of the prepared wood, such as silicone, wax, oil, resinous knots, etc, then dewaxed shellac is very good at adhering to such contaminated surfaces and, once dry, other finishes that are known to fail if applied over those contaminants, will often adhere successfully to the shellac. There's more to it than that, but the above is a potted introduction to some shellac properties.

In your case, if all you want to do is warm up the wood a bit (darken it basically), I wouldn't use Danish oil, which is a form of varnish. I'd just wipe on a light coat of boiled linseed oil and buff of thoroughly, which will give you the same darkening/warming effect, because it's the linseed or tung oil in Danish oil that does the darkening/warming, not the resins and solvents in it . Then leave it to dry for 24 hours or so, and apply the garnet shellac you say you plan to use - it will stick to the dried oil successfully. Whether or not you then apply a wax over the shellac would be optional. Slainte.

 

[ED65]

Yes you can do this, there's no issue with shellacking over oiled wood; in fact it used to be standard practice! Depending a little on the species you're working with there's likely no notable difference between using a blended finish like Danish oil for the oiling step and the linseed oil that would have been the norm back in the old days.

Also the Fat Over Lean rule does not apply in this situation, don't worry about it.

I'm assuming the oil should be sufficiently dry to apply the shellac after sitting overnight in the warm air from my dehumidifier (in otherwise unheated garage).

That would be fine, but actually you don't have to wait.

If you're ever in a tearing rush to finish something you can oil, start building the finish with shellac through the early part of the day, wait for this to harden up some and then complete the finishing and add more protection with a couple of wiped-on layers of poly in the afternoon and evening.