-Post by Gautam Shah
SHELLAC or LAC COATINGS
Shellacs Finishes, were the first true clear coatings. It is believed that Shellac is in use for the past 2000 years. It was used as gum, sealing compound, and as a mastic compound.
Shellac is an insect exudate known as stick-lac. It is refined to remove impurities including waxy substances, and lighten its colour. Button-Lac is a manually purified form and is of darker colour, while machine purified shellac is often de-waxed and de-colourized.
Shellac is soluble in methylated spirit or alcohols. It is a very effective coating material even in very thin viscosity, as a result its penetration and filling capacity is excellent. It is one of the best surface filler material. It is eminently re-coat-able so a very smooth level and glossy surface is possible.
Sankheda furniture (Sankheda near Vadodara, Gujarat, India ) and Chinese lacquer items are examples of shellac coatings.
French Polish has been one of the most popular clear (colourless) coating material. It has been used as wood furniture polish, Protective and glossy coating for oil paintings, besides employed as a paper coating, hair fixer, and as a gum for Gold leaf fixing. French Polish is most preferred conservation coating for old furniture and oil paintings. French Polish on drying does not convert into a non-soluble product. It is technically a non-convertible’ coating system. Once applied it can be removed with alcohol like solvent, without damaging the original surface.
French polish is very similar to natural shellac polish. However resistance to wear and tear is poor, and the film is permeable. But it is re-coat-able material.
French polish includes a number of materials that provide a transparent coating. In the past the most important materials were a shellac, and gum copal. But now a days various pine resins, especially maleic modified rosins of spirit soluble type are used.