This tip has been reproduced from the September 1995 Issue #39 of Faceplate Magazine – The Official Magazine of The National Association of Woodturners NZ Inc. And had been included here in November 2023 with kind permission from the current NAW President.
Preparation of the surface is the key to a good oil\varnish finish. I sand in closely progressive steps with new clean paper. Between the finer stages I wet the surface with water to raise the grain and allow it to dry before continuing with the next grit. On porous hardwoods I avoid blowing the dust out of the grain as it acts as a filler.
The recipe is generally over-rated in importance. I have found that additives like tung oil ( low gloss ) and terebine ( lead poisonous ) only complicate the issue and I have settled on:
1 part gloss polyurethane ( extra for final coat )
1 part alkali refined ( bleached ) linseed oil
1 part mineral turpentine ( sometimes I add vegetable turps for the smell )
Alkali refined linseed oil is preferable to use than ordinary boiled linseed which darkens some woods extensively ( particularly rimu ). The theory is that the turpentine carries the finish into the wood as it penetrates. The oil accentuates the natural colour and figure of the wood. The polyurethane causes the whole brew to set hard, provides a small degree of protection and slows moisture transfer in an out of the wood.
The first application is the most important. Once it has set in the surface very little further penetration occurs with subsequent coats.
Apply liberally with a piece of foam sponge rubber, applying repeatedly where it soaks in, and on end grain. Rubbing the surface energetically with the hands helps it to penetrate. The oil can be left soaking for 15-45 minutes, depending on the day.
Pull your finger through the finish to test for readiness to wipe off. If you leave it too long you may have to apply more oil/varnish/turps to soften the mess. I use one rag to pick up most of the excess and follow with a clean rag.
Rags and foam applicators should be hung up to dry – leave them in a heap and they may ignite.
In summer porous woods should be finished late in the day as the temperature drops. If you apply the finish in temperatures that are too warm you can have problems with the oil/varnish sweating out and settling on the surface. It pays to wipe down again a few hours later and again the next day.
It takes at least three days for the brew to set – one week is better. Re-oiling daily achieves nothing.
When due time has passed polish the surface with fine steel wool ( get some 0000 grade ). Dust off thoroughly and re-apply the mixture. Two applications should look good, three even better. You cannot rush the drying time.
When all the solvent smells have gone you can apply wax, again with foam rubber. After trying just about every brew you can get I have gone back to CO Waxshine which I can get from the local supermarket. The CO wax doesn’t leave streaks like some more expensive brands and brews even if you leave it hours before polishing.
Wax is not a durable surface finish. Water will mark it and the oil/varnish surface fi left laying in a pool. The negative effects are lessened if the wetting during sanding was carried out diligently.
Wax does provide a slipperiness to the surface that may cause a blow or knock to deflect rather than dent. Too much wax provides a sticky mess for dirt to settle in.
I hope this helps you to achieve a good oil/varnish finish that will in time develop patina, unlike a lacquer that deteriorates steadily from the moment of application.
This article first appeared in a club newsletter – guild unknown.