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Expert's Corner — solvent

TIP: Thin Coats vs. Thick, Which Is Better and Why?

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It’s common to hear the instruction that it’s better to apply several thin coats than one thick one. Why is this so? Or is it? What’s involved is drying time, nothing more. Thinner coats of all finishes dry faster than thicker coats. The difference is great enough that you can build the same thickness with several thin coats in less time than you can get that thickness with a thick coat. But the thick coat will eventually dry just as hard and perform just as well as many thin coats. Shellac and lacquer dry entirely by solvent evaporation. The solvent...

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TIP: Patina

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TIP: Patina

Patina is primarily the mellowing and color change that occurs in wood over time due to oxidation from exposure to air and bleaching from exposure to light. Secondarily, patina is the dings, scratches, rubs, etc., that give old furniture character. The mid-nineteenth-century cylinder roll-top desk in the accompanying picture has patina, primarily the bleaching of the mahogany and also the bleaching of the plaster-of-Paris used to fill the pores. The desk has never been refinished, but the finish has been renewed with French polishing. Adding finish on top doesn’t change the coloring of the wood underneath. Patina is highly valued...

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TIP: Differences between shellac and lacquer

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The principle differences between nitrocellulose lacquer and shellac are ease of application and their ability to block off problems in the wood. Both finishes are evaporative finishes, meaning that they dry entirely by solvent evaporation; there is no crosslinking as there is with varnish and catalyzed finishes. As a result, both lacquer and shellac are more vulnerable to being damaged by coarse or sharp objects, heat, solvents, acids and alkalis. Shellac is more vulnerable than lacquer to being damaged by alcohol spills, of course, but keep in mind that beer, wine and mixed drinks are usually very watered down, so...

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TIP: Hot Lye Stripping Is a Job for Professionals

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A common method used for stripping furniture in many professional refinishing and stripping shops is to dip the furniture into a tub full of hot water and lye. This method is relatively inexpensive (compared to using solvents) and very effective. It’s also compliant with many health and VOC regulations that make it difficult to use solvents, especially the most effective solvent, methylene chloride. But you should be aware that old animal hide glue, used on almost all furniture made before the 1950s, dissolves in hot water, and will also dissolve in cold alkaline (lye) water if left in contact for...

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Coating Over an Existing Finish: A Risky Business that Sometimes Works

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Finishes deteriorate as they age. First they dull, then they begin to crack. Exposure to light in the higher ultra-violet ranges, such as sunlight and fluorescent light, accelerates the deterioration. Finishes also get damaged from abuse, which can cause a surface to look bad. In some cases, the only way to repair the deterioration or damage and make the furniture or woodwork look good again is to strip off the old finish and refinish. There are many situations, however, where applying a coat or two of finish on top of what is already there can make the old deteriorated or...

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