Applying a different finish over oil.

[BearTricks]

I turned an extremely spalted sycamore bowl a while ago; I intended it to be used for eating so I applied a simple walnut oil finish, but it's too big for an eating bowl and too small to be a fruit bowl so it's basically just been used to put things in on a sideboard.

The oil has since cured, but I was wondering if I could put a melamine laquer over it to make it a bit more durable. Would adding a new finish over the oil cause any problems?

 

[MIGNAL]

Not sure about melamine laquer. Shellac will go over an oil finish, with a couple of caveats. The oil has to be thoroughly dry/hard, the oil layer needs to be more in the wood rather than sitting on the surface. The 'rule' is soft over hard, rather than hard over soft. Hard over soft tends to lead to craquelure, as the underlying surface has a tendency to move more than the harder, brittle stuff that is sitting on top.
Shellac has a reputation for sticking to everything, which is why it will bond to an oil layer successfully. It's harder than dried Walnut oil though, which is also why it's best to keep the oil layer as thin as possible or just enough oil to pop the grain.

 

[ED65]

Putting another finish over oiled wood is now commonly done. Usually it's not walnut oil but the basic principle holds for any drying or semi-drying oil. I doubt the melamine lacquer will mind the oil in the wood but if you're worried about possibly incompatibility applying an intermediate coat of shellac is the usual safety measure.

 

[ED65]

Shellac will go over an oil finish, with a couple of caveats. The oil has to be thoroughly dry/hard...

I've read this often but I think it's a conventional wisdom that doesn't really bear out in practice. If this were the case people would have to wait a month or more after the last application of oil before they could safely shellac or varnish, and these days most people wait just a day (if that) and it doesn't seem to cause any problems.

Of late there's a finishing regimen sometimes recommended to people in a rush of oiling, shellacking and then varnishing to build up a decent finish in just a single day, two at the outside. After reading about it on another forum I tried it and it worked perfectly well, you'd never know there was wet oil underlying everything.