Shellac
Shellac (/ʃəˈlæk/)[1] is a resin secreted by the female lac bug on trees in the forests of India and Thailand.
[2] It is processed and sold as dry flakes and dissolved in alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish.
Shellac functions as a tough natural primer, sanding sealant, tannin-blocker, odour-blocker, stain, and high-gloss varnish.
Besides wood finishing, shellac is used as an ingredient in food, medication and candy as confectioner's glaze,[4] as well as a means of preserving harvested citrus fruit.
[6] Most European languages (except Romance ones and Greek) have borrowed the word for the substance from English or from the German equivalent Schellack.
[12] The raw shellac, which contains bark shavings and lac bugs removed during scraping, is placed in canvas tubes (much like long socks) and heated over a fire.
The end-user then crushes it into a fine powder and mixes it with ethyl alcohol before use, to dissolve the flakes and make liquid shellac.
Alternatively, old shellac may be tested to see if it is still usable: a few drops on glass should dry to a hard surface in roughly 15 minutes.
Luthiers still use shellac to French polish fine acoustic stringed instruments, but it has been replaced by synthetic plastic lacquers and varnishes in many workshops, especially high-volume production environments.
[16] Shellac dissolved in alcohol, typically more dilute than as used in French polish, is now commonly sold as "sanding sealer" by several companies.
With a melting point of 75 °C (167 °F), it can be classed as a thermoplastic used to bind wood flour, the mixture can be moulded with heat and pressure.
When dissolved in alcohol (typically denatured ethanol) for application, shellac yields a coating of good durability and hardness.
An article from the Journal of the American Institute of Conservation describes using infrared spectroscopy to identify shellac coating on a 16th-century cassone.
[24] In the early- and mid-twentieth century, orange shellac was used as a one-product finish (combination stain and varnish-like topcoat) on decorative wood panelling used on walls and ceilings in homes, particularly in the US.
In the American South, use of knotty pine plank panelling covered with orange shellac was once as common in new construction as drywall is today.
[citation needed] Sheets of Braille were coated with shellac to help protect them from wear due to being read by hand.
[citation needed] Shellac was used from the mid-nineteenth century to produce small moulded goods such as picture frames, boxes, toilet articles, jewelry, inkwells and even dentures.
For multi-layer windings, the whole coil was submerged in shellac solution, then drained and placed in a warm location to allow the alcohol to evaporate.
The shellac locked the wire turns in place, provided extra insulation, prevented movement and vibration and reduced buzz and hum.
Mixed with other resins, barium sulfate, calcium carbonate, zinc sulfide, aluminium oxide and/or cuprous carbonate (malachite), shellac forms a component of heat-cured capping cement used to fasten the caps or bases to the bulbs of electric lamps.
[citation needed] It is the central element of the traditional "French polish" method of finishing furniture, fine string instruments, and pianos.
Although its durability against abrasives and many common solvents is not very good, shellac provides an excellent barrier against water vapour penetration.
[39] Naturally dyed silk cloth, including that using shellac, is widely available in the rural northeast, especially in Ban Khwao District, Chaiyaphum province.
