Michael Dresdner » varnish

Jewelry finish

Michael — Wed, 24 Nov 2010 17:18:07 +0000

Q: What would be the best non toxic finish I could use on jewelry made from wood?
A: I’m not sure what you mean by non-toxic, as that is a term used typically for things we ingest.
If you mean that the finish itself is edible or drinkable in its liquid form, that would include raw linseed oil (but not boiled linseed oil), mineral oil, which is a wood treatment but not a finish, shellac cut into pure ethanol, which is potable but intoxicating, and any plant or animal wax, such as beeswax, with no solvent added to it. None of the above would make particularly good finishes for jewelry, for a variety of reasons.
Of course, pretty much any finish is non-toxic once it cures, since most are simply inert plastics once they dry, and we don’t generally have the ability to digest plastic. Eat it and it will pass right through you.
If, on the other hand, you mean non-reactive, meaning finishes that typically do not cause allergic reactions on the average person’s skin, that varies tremendously with the individual and what he or she is allergic to. Still, except for nut oils near people with nut allergies, I don’t know offhand of any finish that causes skin irritation, but admittedly, there are people allergic to darn near everything out there.
Personally, I would go with an oil based varnish or oil based polyurethane. They are durable, are not affected by skin oils, acids, bases or heat, and will not react or soften in contact with perfumes, skin creams or nail polish remover.

Circa 1920

Michael — Wed, 10 Nov 2010 14:00:19 +0000

Q: I have a circa 1920 chiffarobe I would like to refinish. I stripped it with alcohol and sanded to 220. I have never been very successful with shellac. What would you suggest for a finish what would give a reasonable look and protection?
A: What I would suggest is what it had originally, and if the finish came off with alcohol, that pretty much confirms it was shellac. Since you have, as you say, never been very successful with it, you have three obvious choices; learn to use it (it’s actually a very easy finish to use, if someone shows you the ropes), take it to someone else to finish, or apply a non-original finish. If you choose a non-original finish, it should, of course, be any finish you do have success with. In case you were concerned with period authenticity, the other finishes in common use for furniture in the 1920’s were oil varnishes and nitrocellulose lacquer.

Auntie Oxidant

Michael — Fri, 24 Sep 2010 14:00:07 +0000

Q: I made some replacement handgun grips of cocobolo. Realizing that cocobolo has a lot of natural oils in it I first sealed it with shellac, then filled the pores with a product called z-poxy. I then sanded and applied one coat of Minwax polyurethane. Three weeks later I can make a thumb print in the finish. I think I sanded through my seal coat, because the poly is not curing. Can I remove the uncured poly with mineral spirits?
A: I doubt it, unless it is still fully liquid. What typically happens is that exposure to the raw cocobolo (where you sanded through) will inhibit the cure of an oil based finish, but not keep it entirely liquid. Thus, it stays tacky or gummy.
You’re certainly welcome to try scrubbing off the finish with mineral spirits on a coarse nylon abrasive pad, but in most cases you will have to resort to at least refinisher if not stripper. Since the parts are so small that should not be a big deal. You can also sand back to raw wood, again, since the parts are so small.
For the record, the reason oil based finishes don’t cure over dalbergias, such as cocobolo, has nothing to do with the wood appearing oily. In fact, it contains resins, but not, strictly speaking, oils. The problem is that the wood also contains a natural anti-oxidant.
Think of how citric acid, another natural plant anti-oxidant, slows the oxidation and browning of freshly cut apples if they are dipped in lemon juice. The anti-oxidant in dalbergia woods does the same thing.
Oil based polyurethane and varnish cure by oxidation polymerization; they take oxygen from the air and use it to link up small molecules to make large ones, thus turning a liquid finish into a solid film through chemical linking. The anti-oxidant is the culprit in delaying or preventing that chemical reaction.

Lacquer vs. oil based

Michael — Fri, 20 Aug 2010 14:00:22 +0000

Q: You make a distinction between lacquer and oil based finishes. Why does it matter?
A: Lacquer, which is a category that includes shellac, is an evaporative finish. It cures solely by the solvent evaporating. That means the molecules floating around in the solvent when it is in its liquid form are exactly the same once the solvent evaporates. The film is formed by these long, gangly molecules twisting and clumping together, but not bonding chemically. Technically, they form an amorphous solid.
Because of that, evaporative finishes have two very distinct characteristics. First, they will redissolve with their own original solvent; lacquer with lacquer thinner, shellac in alcohol. Second, when subjected even to fairly low levels of heat, they start to liquefy. Hence, they are known as having poor solvent and heat resistance.
Oil based finishes cure very differently. They actually go through a chemical change in which small molecules link up and form larger molecules, eventually forming a solid. Though most do, an oil based finish does not need to have solvent in it to work. A good example of a solvent free finish is pure boiled linseed oil. Although no solvent evaporates, it goes from liquid to solid, using oxygen absorbed from the air to bond its molecules chemically. Epoxy, conversion varnish, polyester, UV coatings and even some types of polyurethane all bond through chemical reaction rather than solvent evaporation alone. Such finishes will not dissolve in their original solvent, and typically are thought of as having much higher chemical and heat resistance.

Hold on there, finish!

Michael — Tue, 25 May 2010 14:00:38 +0000

Q: What finish will stand up to New York winters? Sometimes the windows sweat on the inside and my finish comes off in a year or two.
A: Part of that my be your choice of finish, but it may also be the preparation. You must start with clean, sanded wood to get good adhesion, then choose a finish that is not prone to peeling and has a high moisture resistance. I’d go with oil based varnish, spar varnish, or exterior oil based polyurethane. All have good adhesion and resistance to moisture delamination.

Bartley gel it is

Michael — Thu, 13 May 2010 14:00:51 +0000

Q: The Rockler gel urethane I used to use is no longer available. Any suggestions?
A: The Rockler gel was a private label product made by Lawrence McFadden. They went into bankruptcy and their formulas and remaining product was purchased by Seagrave Coatings. Peter Teppermann, the president of Seagrave, assured me that they will continue selling the product under the Bartley label, but not under the Rockler label, at least for the present. Thus, go ahead and buy the Bartley gel, made by Seagrave, and you will find it is the exact same product you are used to using in a Rockler can.

Bubbles? Champagne, not varnish

Michael — Thu, 01 Apr 2010 17:00:28 +0000

Q: How do you prevent bubbles in spar varnish? I have tried bristle brushes, sponge brushes, and even putty knives.
A: In real estate the adage is location, location, location. With brushing oil based varnish, it’s technique, technique, technique.
A few basics come first. Start with the softest natural bristle brush you can find; ox hair is ideal, but ox hair blends, which are more available, will also work well. Stir the varnish, pour some out into a square pan, and reduce it at least 15% with mineral spirits. Soak the brush up to the ferrule in mineral spirits before you begin; then squeeze out the excess, and dip only the last one third of the bristles into the varnish. Touch the tips of the bristles to the flat side of your square pan; this will leave the brush loaded, but not dripping.
Touch the tips down gently at 45 degree angle and gently press to deflect the bristles as you start to move. This will cause the finish to rise to the top of the bristles; the area you see looking down onto the brush. The object is to then gently slide the brush out from under the finish.
You will notice I said gently more than once. Brushing is a calm, Zen activity. Focus, think about letting the fluid flow, and whatever you do, don’t scrub with the brush.
There’s more, but it really requires a photo essay, and I can’t do that here in this blog. However, I have done it in several books and in a DVD, if you’d rather see it in action than in a series of still photos. You’ll find very good brush work teaching, including how to clean and preserve brushes, and even how to buy brushes, on pages 25 – 31 and 128 – 131 of The New Wood Finishing book, and on pages 63 – 69 in Wood Finishing Fixes. Page 67 of that book, which is a Q&A format, begins “How do I eliminate bubbles in brushed finishes?” You can find both the books and DVD in the books and videos section of this blog.

The right size

Michael — Wed, 24 Mar 2010 17:00:11 +0000

Q: Here in my country there is only one kind of gold size; a waterbased size which is white in the can and cures colorless and gloss. We have to thin it with water and apply it with a little cotton ball. This process of applying the size takes a lot of time and sometimes is not satisfactory. Can I spray the size instead, or can I use high quality varnish as gold size?
A: Yes to both. Virtually all waterbased coatings spray quite nicely even without being reduced, and oil varnish can indeed be used as size. The key is to catch it just at the right point of drying, when it is dry enough to work on but still tacky enough to adhere to the leaf. Varnish itself is a mixture of drying oil and resin. Most oil based gold size is nothing more than long oil varnish. That means it contains slightly more oil than resin. You can even modify an oil varnish by adding a small amount of boiled linseed oil, about three ounces per quart, to the varnish to convert it to a long oil varnish.

We don’t need no stinkin’ scratches

Michael — Wed, 10 Feb 2010 17:00:56 +0000

Q: There’s a method I want to try; waterbased dye, seal, gel stain left dark in corners and wiped to simulate wear, top coat. How can I brush top coat using varnish without screwing up the gel, since varnish needs scratches to hold to?
A: No it doesn’t. Just let the gel dry thoroughly so that it does not get moved around by the brush, and flow the finish off the brush as opposed to scrubbing. That technique will allow you to easily topcoat this sort of glazed finish without any problems, and oil based varnish will easily adhere to dried oil based gel stain.

Glazed over

Michael — Fri, 18 Dec 2009 17:00:42 +0000

Q: Would Mohawk Finisher’s Glaze be safe to use over shellac, spirit varnish and oil varnish, considering it contains methanol?
A: Yes. The amount of methanol in the mixture is very low, and you would probably have no problems at all. About the worst that would happen is that it would bite more aggressively into alcohol soluble finishes such as shellac. That means you must work more quickly, and may not be able to wipe off the glaze completely should you change your mind. Incidentally, there is some disagreement about the definition of the term spirit varnish. Some insist it means any varnish that cures solely by solvent evaporation, while others point out that historically, it was often used as simply another term for shellac.