Michael Dresdner » lacquer

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.

Lacquer and d-limonene

Michael — Tue, 14 Sep 2010 14:00:40 +0000

Q: I need to know if d-limonene will harm cured nitrocellulose lacquer. I want to use it as a solvent in a 25% mixture with mineral spirits.
A: No, d-limonene will not harm lacquer. It is one half of the racemic mixture called dipentene, and for all intents and purposes as far as finishing and cleaning are concerned, it is completely interchangeable with mineral spirits. There’s no difference in how they behave. The only real difference would be price due to derivation; inexpensive mineral spirits comes from petroleum, while the decidedly more expensive dipentene is extracted from citrus fruit peel.
In case you were curious, the d-, which stands for dextrorotatory, or right hand rotation, is generally lower case in chemical notation. It’s fellow traveler in the racemic mixture is l-limonene, for levorotatory. Racemic mixtures contain equal amounts of left and right mirror image versions of the same molecule.

Bleeding sunburst

Michael — Mon, 06 Sep 2010 14:00:53 +0000

Q: I stained a guitar red/brown using water soluble dye. After the stain was dry, I dry brushed dark brown water soluble dye around the edges, fading toward the center for a sunburst-like finish. Clear lacquer coats finished the job. Will the dyes bleed into each other over time and become unattractive?
A: No. Water soluble dye will not bleed into solvent based lacquer. It will bleed into waterbased finish, though. However, bleeding is not your main problem.
Dye without binder added, as is typical for water soluble dye, will dry back to a powder once the water is gone. Thus, the strategy is to let it soak into wood, but wipe off anything that does not soak in. Dye brushed onto the surface and left there will dry and leave a layer of powdered crystals on the wood’s surface. That could cause future coats to delaminate, since they can’t adhere to a layer of powder unless they are able to dissolve it, and solvent based lacquer can not dissolve water soluble dye. In short, you have set the stage for your finish to peel at some future date.

I’m melting!

Michael — Wed, 01 Sep 2010 14:00:18 +0000

Q: I learned the hard way that a thin plastic cup I had could be dissolved by lacquer thinner. Can you tell me what kind of plastic container will not react and how I can tell a container is made of a safe plastic?
A: Nalgene, nylons, polyesters, acetal, polyethylene and polypropylene all have decent resistance to lacquer thinner. I gather you are using recycled food containers, like yogurt cups and the like. You can do a lot of research and figure out which plastic is being used based on the recycle codes http://www.earthodyssey.com/symbols.html or simply do it the quick and easy way; test your container first with a bit of thinner.

Acetone and the VOC question

Michael — Tue, 31 Aug 2010 14:00:47 +0000

Q: I found some conflicting information on thinning nitrocellulose lacquer. Some very good finishers use straight acetone while others write of using lacquer thinner. I realize lacquer thinner is a soup so there are many possible formulations, but generally I was wondering how acetone might behave differently from thinner.
A: Acetone, a ketone, is one component of lacquer thinner. Others include esters, glycol ethers, alcohols and possibly aliphatic hydrocarbons. Each component has a particular task, and in some cases, a mixture or variety will be a more effective solvent. A lot depends on the resins in the lacquer itself. The manufacturer of the lacquer will know what the best thinner mix will be, which is why some lacquers come with specific thinners likely to work better than the wide spectrum ones available in home and paint stores.
One trend in the industry is to reduce VOCs, either for green reasons or to placate EPA inspectors. Acetone is an exempt solvent, thus it is not, legally, a VOC. For shops trying to reduce their VOC output, using acetone instead of lacquer thinner is a useful strategy.
Generally speaking, acetone is a faster solvent than most lacquer thinner mixtures. It’s rarely as effective as a wide spectrum solvent. Thus, adding acetone alone will most likely change the way the finish behaves. Whether it is better or worse for your style of spraying and finishing needs is a very subjective question. Try it and see if you like it better. I should warn you, though, that some lacquers, such as those that require high levels of glycol ethers as their primary solvent, will not behave as well with an overabundance of acetone in the mix.

What’s in a name?

Michael — Tue, 24 Aug 2010 14:00:26 +0000

Q: How does enamel differ from lacquer?
A: The term lacquer refers to how a finish dries. Specifically, it means a coating that dries solely by solvent evaporation. It does not give any clue to what resins were use in it, though of course, certain ones are particularly common.
The term enamel has no definitive meaning in coatings anymore, though it did at one time. Today, the term is simply used to mean a very durable paint, without giving any indication whether it is reactive, such as an oil based enamel, or evaporative, such as a lacquer enamel, or a multi-phase coating that has elements of curing methods.

Over pre-catalyzed

Michael — Sat, 21 Aug 2010 14:00:05 +0000

Q: Can you apply brushing lacquer over sprayed pre-catalyzed lacquer?
A: That depends on the pre-catalyzed finish, and how long it has been cured. In some cases you can; in others you risk cracking and wrinkling. Because it is so risky without knowing a whole lot more about the particular coating involved than anyone outside the formulator’s lab is likely to know, I would not advise it.

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.

Oil based lacquer?

Michael — Thu, 19 Aug 2010 14:00:04 +0000

Q: Can I put oil based wiping polyurethane over oil based spray lacquer?
A: The simple answer to your question is yes, you can put oil based polyurethane, whether wiped, brushed or sprayed, over almost anything, including lacquer. For the record, though, lacquer is, by definition, an evaporative finish, while oil based finishes are, by definition, reactive. In other words, the terminology indicates the process by which the finish goes from liquid to solid film. Thus the term “oil based lacquer” is at best a misnomer. While one could make an evaporative finish using a stable resin derived from oil, that should still be called simply lacquer.