Shellac base coat, help me understand...

[Jeff L Jump]

I've been finishing wood projects for a number of years now, it's my favorite part of a project. I use shellac a lot and love it. I frequently read others who describe a finish process using shellac as a base coat and following up by topping the shellac with a BLO or other oil, or poly finish, presumably to get the grain to pop with the oil. If...shellac also being considered a seal coat (my understanding), then how is the application of a layer of oil finish over shellac going to cause the grain to pop. As I see it, you get the pop from the shellac to begin with so topping with an oil finish wouldn't add any additional visual impact, as people suggest is the purpose of topping shellac with an oil finish. Or does it? Do I have this wrong?

[Doug Hepler]

Jeff,

You are correct that the BLO won't pop the grain if applied over shellac or any other film forming finish. I have not heard until now of anyone advising BLO over shellac, so I'm curious about where you got this impression. I often pop grain with a thin coat of BLO on bare wood, left to soak in, scrubbed off, and left to dry overnight. I never apply BLO over a film finish as part of a finishing schedule because I think it would not add anything except the possibility of making a mess. Some people use various mixtures containing BLO as a "miracle finish restorer" for old finishes. I don't because the BLO doesn't ever dry hard and makes the surface sticky and attractive to dust.

Think of BLO as a very mildly tinted oil stain. It soaks into and colors pores and earlywood more than latewood and heightens the contrast. Shellac does the same thing, to a lesser degree if it is lighter in color. Both BLO and shellac also affect the reflective properties of the wood.

[John TenEyck]

BLO first followed by shellac is a common finishing process, never the other way around. Personally, I almost never use BLO.

John

[Wayne Lomman]

You have it right. Your shellac is doing the job. I don't use BLO for anything other than cricket bats and axe handles. The colour and effect is achievable with stain and clears. Cheers

[Jeff L Jump]

Thanks all, that's what I wanted to know. I've not read of anyone specifically stating they were putting 'BLO' over shellac, but I've read people describe using oil over shellac. BLO being so common of the drying oil finishes, I assume when someone is describing an oil finish, it's probably BLO. But I got what I needed. Thanks again.

[Patrick Chase]

Thanks all, that's what I wanted to know. I've not read of anyone specifically stating they were putting 'BLO' over shellac, but I've read people describe using oil over shellac.

Oil over shellac doesn't make sense in general. Oil-based varnishes *do* make sense over shellac, but people usually call those out as something other than just "oil", specifically to avoid this sort of confusion.

The difference between the two is that oil-based varnishes are film-building due to their resin content, while pure oils (Linseed, Tung, etc) are not. Shellac is also a film-building finish, and as a rule it does not make sense to use a non-film-building finish such as oil over a film-building one. The only exception I know of is for polishes/waxes, but you wouldn't want a polymerizing oil there. All it will do is form a layer of rubbery gunk over your perfectly good shellac film.