BLO versus polymerized oil finish

[Jules Dominguez]

I've used Watco Danish Oil finish over the years as the only finish on cherry and other woods in the belief that it not only gives you the natural oil-finished appearance, but also hardens the wood. My perception is that it actually does harden the wood, but I've never tried to scientifically test that. I notice from a lot of posts that most Creekers seem to use BLO. The Watco is very expensive, I assume much more so than the BLO. Other than cost, what are other pros/cons of BLO versus Watco?

[Jim Becker]

Watco is a varnish oil. (Oil and varnish in combination so you get the "benefits" of each at the same time, at least for the initial coat) It doesn't "harden the wood". "It" cures like any other varnish oil and that gives you the perception that you have something harder because you in fact, have a film finish. Just a thin one.

BLO is just linseed oil with metalic driers. It also cures, but not as "hard" as varnish. That's why many folks prefer to top coat it with other products when they want a "harder" wear layer on their project.

[Jules Dominguez]

Jim, I understand that the Watco formulation contains something more than just "pure" oil, but I don't believe that it forms a surface coat. I think whatever is in the Watco is absorbed into the wood fibers. When I use it, I wipe it down very thoroughly, finishing with a dry cloth. If any oil is inadvertently left anywhere on the surface, it dries to a hard shiny gloss, which is unfortunately very visible and requires sanding to remove.
I think that the "curing" or "hardening" of properly-applied Watco occurs within the fibers and thus does make the wood harder. And I think that the polymerization process adds hardening in addition to the hardening provided by the resins in the oil. My experience is that a Watco finish is very durable and I've never had to re-finish, even after as much as 15 years.
I probably should have taken more trouble with formulating my post. My question boils down to "why would you use a three or four coat finish (BLO-shellac-wax or poly) when a one coat finish provides adequate protection by itself. I assume that the answer is that the BLO-shellac-etc. finish is deeper and more attractive in appearance. Watco by itself provides a natural-looking but admittedly dull finish. Is that correct, or are there other points that I'm missing?

[Jim Becker]

I've used Watco on many turnings with multiple coats and it provides a film finish that builds...and buffs out wonderfully. It's a nice finish product and yes, it's easy since you can finish with just one product. But if you take almost any oil-based varnish and add it to equal parts BLO and mineral spirits, you'll have pretty much the same thing.

Polymerization is pretty much a heat process that pre-starts chemical cross linking for a quicker cure. This is what the Tried and True folks do to their oil product to make it cure rather than add metallic driers. Lee Valley sells a Tung Oil product that is polymerized so that it will cure in a few days, rather than over weeks as pure tung oil normally takes. In fact, I'll go so far to say that the mere act of manufacturing varnish involves polymerization as there is heat involved to change the individual raw materials (oil, resin, etc) into the varnish, itself. It's "oil based" but there is no oil left once it's varnish. In the case of Watco and similar, they have mixed varnish with oil and thinner. The oil penetrates and pops the grain while the varnish (which is thinned) also penetrates and cures a little harder than the oil would by itself.

I do like it when you said, "My question boils down to "why would you use a three or four coat finish (BLO-shellac-wax or poly) when a one coat finish provides adequate protection by itself?" because you raise the point I made in my very first introductory rant in this forum when it was created...what is the "definition of protection". I hope you ask this for every project you create! What is the minimum I need to do to this beautiful wood to help it survive what it is expected to do? If it's going to sit on a shelf and collect dust, why slather it in plastic. Oil and Wax may be all you need! Your kitchen table is a different story and there are different expectations. My little side table recently created for my office just has five or six wiped on applications of Waterlox. (Similar to your Watco, except phenolic varnish based) It was quick and easy. My side tables and "coffee table" in the TV room have shellac finishes and have survived our two Russian daughters' visit this month with flying colors. My kitchen table has Watco as the base with about 12 coats of wipe-on MinWax Polyurethane varnish. It has a couple scratches (from a contractor's stupidity, not from normal use)

Bottom line...if you like the look of the Watco, use it. It's a good finish. If you like it but want more sheen...put on more coats. One is not enough.

[Jules Dominguez]

Jim, I made you reach a little deeper that time, didn't I? Thanks