Woodworker's Journal 2009-33-4, страница 48
ABOUT MICHAEL DRESDNER Finishing Hotline A Lacquer That's Cool with Cold By Michael Dresdner I built a grandfather clock using purple-heart. I went to an automotive supply store to get lacquer and they told me that automotive lacquer would not work, I needed furniture lacquer. What is the diffcrcncc between automotive and furniture lacquer? Don Ackerman Flint, Michigan Nitrocellulose (furniture) lacquer, when exposed to extremes of heat and cold, is likely to crack. Contact us by writing to "Finishing Hotline," Woodworker's Journal, 4365 Willow Drive, Medina, MN 55340, by faxing us at(763)478-8396 or by emailing us at: finishing@woodworkersjournal.com Please include your home address, phone number and email address (if you have one) with your question. Michael Responds: Automotive lacquer is made to tolerate wider ranges of heat and cold without cracking than is most furniture (nitrocellulose) lacquer. For that reason, furniture lacquer will not work well in outdoor applications, such as on cars, but the reverse is not true. Automotive lacquer will indeed work on furniture. In fact, many guitars, which tend to go from heated indoor areas to cold car trunks over and over, are often finished in automotive lacquer for just that reason. i ^ J I build, restore and repair wood and canvas canoes and use spar varnish on all exposed wood surfaces. I also use varnish on some indoor jobs: for example, I have always liked the gentle warming of color Michael Dresdner is a nationally known finishing expert and the author of The New Wood Finishing Book from Taunton Press. When not writing about woodworking, he is an active community theater Editor Rob Johnstone should have learned that automotive lacquer protects guitars when repeatedly moved from hot to cold environments. The first guitar he made suffered from finish cracks due to extremes in cold and heat. that varnish gives to pine paneling. I have noted that varnish cans, though appearing to be no different than other paint cans, are often difficult to close securely. Arc the cans really different? Related to that question, varnish always forms a skin when a can is left on the shelf for some time, even if the can is sealed securely. What causes that skin and can it be prevented from forming, thereby giving the varnish longer shelf life? Roger A. Powell Raleigh, North Carolina Michael Responds: No, the cans are not any different. As for the skin, it is caused by the same thing that causes the finish to cure: oxygen. In this case, it comes from the air in the space above the finish, called the "headroom" in finishing parlance. Oil varnish is an oxygen polymerizing finish. That means it takes oxygen from the air and uses it to crosslink the finish molecules, turning them from a liquid into a solid. The skin is simply cured 68 August 2009 Woodworker's Journal |
