Finish Preview

[transatlantic]

From what I have seen, when using an oil based finish, you can rub down mineral spirits (white spirit?) to see what your finish will look like before actually applying the oil, to bring out any defects like left over glue or what not, to remove.

I've also seen that for Shellac, you are supposed to used denatured alcohol, which I believe is meths?

If I'm using a water based varnish, would I just use water for this instead? I'd guess that water will take a lot longer to dry and will cause the grain to rise more than the other liquids?

 

[yetloh]

If I'm using a water based varnish, would I just use water for this instead? I'd guess that water will take a lot longer to dry and will cause the grain to rise more than the other liquids?

If you want to see what the efffect of finish will be it doesn't really matter what you use, but I wouldn't use water for the reasons you mention. White spirit or alcohol will do. I'm not sure that you really can get a true preview with WB finishes because, from my experience, these tend to sit on the surface and give a very cold, dull look. This can be largely avoided by applying a coat of shellac before applying the WB fiinish. It's worth experimenting on an offcut. Also, it's worth knowing that pretty much any fiinish will "take" over shellac.

Jim

 

[dzj]

Yes, experimenting on an offcut is a good way forward. I always try out my finish on a couple offcuts,
as just one isn't usualy representative of the whole piece you're making.

 

[worn thumbs]

I would echo the comment about water based varnish being a bit lifeless.I had a bad experience with it and a couple of years ago I was planing some boards that a designer pal intended to use for shelves in his office and when I asked him what finish was planned,he said "anything but water based".The diy sheds all push it quite hard though.If you've already bought it you might be stuck with it.The use of shellac can be good,but doesn't quite bring out the richness of the wood in the way that a more traditional varnish will.I will admit that for most household surfaces I use Ronseal Satincoat as it gives a good colour and is pretty durable as well as being shown in it's true colours by white spirit.

 

[transatlantic]

Ok, so I appreciate that I won't get a good idea of the finish, but what about bringing out the defects? What should I use for doing that for water based and poly based varnishes? White spirit?

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[worn thumbs]

Water should work,just be prepared to flatten the grain with fine paper after it has been moistened as it will likely swell.

 

[ED65]

...mineral spirits (white spirit?)

Yes mineral spirits is the American name for white spirit. You may sometimes see references to Stoddard solvent which is also the same thing.

I've also seen that for Shellac, you are supposed to used denatured alcohol, which I believe is meths?

Yes meths is our version of denatured alcohol, or DA for short. DA and meths are not always exactly the same thing, but for this they're taken to be equivalent

You can use an alcohol to preview before shellac but many still use white spirit despite it taking longer to evaporate.

If I'm using a water based varnish, would I just use water for this instead? I'd guess that water will take a lot longer to dry and will cause the grain to rise more than the other liquids?

You can use water for a preview of finish but not for a preview of water-bourne finishes. AFAIK there isn't anything you can use to give an accurate preview of those, other than tests done on scraps from the project, or the undersides or backs of the thing you've built.

When using a water-bourne finish many wet the wood in advance anyway to raise the grain, but you can just let the first coat of finish do that and knock back at that stage if you'd prefer.

Ok, so I appreciate that I won't get a good idea of the finish, but what about bringing out the defects? What should I use for doing that for water based and poly based varnishes?

If I may, the thing to aim for is not to need to preview to highlight defects. Your glue cleanup processes and general methodology should prevent glue contamination of show surfaces, and careful scrutiny of the piece in good light (preferably daylight if available) will highlight any textural issues better than wetting.

 

[yetloh]

If I may, the thing to aim for is not to need to preview to highlight defects. Your glue cleanup processes and general methodology should prevent glue contamination of show surfaces, and careful scrutiny of the piece in good light (preferably daylight if available) will highlight any textural issues better than wetting.

I agree. Even better for defects is to look across the board at a lowish angle using a raking light. Glue contamination can be a real problem - it shows up as a lighter patch where the glue has effectively sealed the surface. Look carefully for this effect when previewing and sand or scrape to remove any patches.

Jim

 

[transatlantic]

Thanks guys. For me though, defects aren't just glue, but alos areas perhaps where I have a little tearout that is hard to detect by eye, but will be very blotchy when you apply a stain for example.

 

[ED65]

Very easy to spot even minor tearout, and other shallow defects, in raking light. It works so well actually you have to learn what you can safely ignore!

If you're hand planing and getting minor tearout have you tried moving the cap iron closer to the edge? Under half a mil is my standard setting now for a no. 4 and I sometimes move it closer than that. If for any reason you can't use this scrape your show surfaces.