Michael Dresdner » clear coat

Don’t make me blush

Michael — Wed, 01 Dec 2010 14:00:56 +0000

Q: I need to finish a reproduction 17th Century Chester County Spice box. How much trouble will I have if I take the box into the unheated garage long enough to spray shellac with an HVLP and, then take it right back into the house? Will I end up with blushing?
A: Not likely. However, if you do, simply spray it again and the blush will go away. The truth is that you probably will have no problems whatsoever.

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.

Over toning lacquer

Michael — Thu, 11 Nov 2010 14:00:06 +0000

Q: I used a toning lacquer to color the wood. I want to put polyurethane over it. Can I do this?
A: Yes, you can.

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.

Pen polish

Michael — Mon, 08 Nov 2010 14:00:07 +0000

Q: I am new to pen turning. Can you recommend some finishes?
A: It depends largely on the pen material. Obviously, cast acrylics need no finish and can simply be buffed. Ditto for very hard or resinous woods, like rosewood, ziricote, bocote, cocobolo, lignum vitae, ebony and even boxwood. For other woods, I tend toward simple finishes; just wax, or wax over boiled linseed oil or wipe on varnish. For a very durable finish, I also like either cyanoacrylate (CA), or a combination of boiled linseed oil and CA. The CA will instantly cure the oil into a hard solid film. Using paper towel applicators on the spinning lathe, apply a thin coat of one, then the other immediately. Add as many coats as you like, sanding for smoothness when necessary. Once cured, which takes only minutes, this finish will buff nicely.

Making an impression

Michael — Tue, 26 Oct 2010 14:00:06 +0000

Q: I am pre finishing a large two piece conference table. I finished spaying a heavy coat of my last application of flat pre cat over two coats of vinyl sealer and two coats of flat. The temperature here is in the 80’s with about 28% humidity. I plan on wrapping these tops in shipping blankets laying one on top of the other for a 1500 mile delivery. How long should I wait until the finish is hard enough not to mar or rub?
A: That’s not as simple a question as it appears. There are two variables that you did not tell me, so the best I can do is give you a rubric for figuring it out, and that includes explaining the cure variables you are working with.
First, understand that catalyzed, and especially pre cat mixtures, vary tremendously in cure time depending on their formulation. Specifically, the higher the acid content the faster the cure, but there is no standard. Thus, you need to read the spec sheet; it should tell you when full cure occurs. Typical formulas can range from as little as eight hours to eight days, and that’s for one coat on an already cured surface. That brings us to number two.
Second, this will all change if the four base coats of vinyl and flat were not catalyzed. If they were not, it greatly extends the time needed to prevent blocking. As I said, since I am lacking these critical bits of information, I can’t give you a solid time. However, it won’t hurt to do a thumbnail test. Find an inconspicuous spot and press a thumbnail into the finish with more pressure than you suspect will be exerted by the shipping weight. That will at least give you insight into how the finish is geared up to resist an impression from the pads.

Bartley clear gel

Michael — Mon, 25 Oct 2010 14:00:34 +0000

Q: I recently purchased a quart of Bartley Gel Varnish over the internet. The product I received is Bartley Gel Stain – Clear Satin. Is this the same as the Bartley Gel Varnish?
A: Yep. The best I can figure is that Bartley started as a one step wipe on stain and finish, sold as an “all you need do is wipe on the stain and you’re done” panacea. That started people referring to what was actually a tinted finish as a stain. It made sense to keep the familiar name for the clear version. The same gestalt exists in deck coatings; most are technically tinted finishes, but are called stains.

Bigleaf, big pattern

Michael — Tue, 28 Sep 2010 14:00:07 +0000

Q: I am making a cabinet door of solid cherry with a quilted maple panel. I want a bit of contrast between the cherry and maple and to show off the quilting in the maple. I was planning to stain the maple with a cherry color oil based stain and sand it lightly with 600 grit before applying wipe on polyurethane on the entire door.
A: Most quilted maple is western bigleaf maple, and unlike its eastern rock maple cousin, will absorb some pigmented stain. However, the ideal way to intensify grain in maple is to go with something that has a lower molecular weight. In the case of stains, that would be dye. A weak dye, flooded on and wiped off, will intensify the quilt pattern as well as adding color. Of course, an oil based finish, such as wipe on polyurethane, will add a slight amber color, which will also intensify the grain. In short, you don’t need stain to bring out the grain, though if your goal is to change the color to match the cherry, yet still pop the grain, dye is the way to go.

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.

Kitchen magic

Michael — Thu, 16 Sep 2010 14:00:38 +0000

Q: The kitchen cabinets in my 20 year old house were painted rather than stained. They are a cherry color on what I believe is alder. Over the years some of the paint has chipped away leaving behind part of the original unfinished wood. The cherry paint itself is not a solid color, but varies in color a bit. Can a handy person do a decent patch up job?
A: Absolutely, but it helps to know what you are dealing with, and it’s not paint. It’s called toner, which is clear finish with some color added to it, though not as much color as would be in an opaque paint. Instead of staining the wood, the wood is sealed, then sprayed with layers of semi-transparent color until one gets a uniform tint. Spraying more means darker, more opaque color; less gives lighter, more translucent color.
Because that is such a common method of coloring cabinets and furniture, there are common repair materials available to do touch up. They come in two distinct types; pens and aerosol cans. Touch up pens are essentially felt tip markers made in common furniture finish colors. You use them just as you would a marker, simply coloring in the light areas to match. You can also find aerosol cans of toner or tinting lacquer which you spray on the area to blend in the color. Both are quite easy to use. Just make certain you clean the area, or better yet, the entire cabinet, with a good degreaser first to ensure good adhesion. The cheapest effective cleaner is mineral spirits, also sold under the name paint thinner.