Varnishes
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Varnishes are liquid coatings containing a resin dissolved in an oil or solvent that form a protective film. They are used as decorative and protective coatings on wood and painted surfaces. The key ingredients are a resin such as rosin, copal or shellac dissolved in a solvent like linseed oil, turpentine or spirits. Different types of varnishes are used depending on the solvent - oil varnishes dry slowly but are durable, turpentine varnishes dry quickly but are less durable, and spirit varnishes containing shellac are commonly used for furniture. Japans contain asphalt and are applied to metal surfaces. Varnishes protect surfaces from moisture damage and weathering while enhancing the natural
Varnishes
- 2. Definition • A Varnish may be defined as a “homogeneous liquid Containing essentially a resinous substance dissolved in a suitable oil or a volatile liquid”. A Varnish does not contain any pigment. However it is always used as a finishing coat.
- 3. Varnish
- 4. Function of Varnish • More Commonly a Varnish is used over a wooden object as a decorative & Protective Covering. • The Varnish brings out the grains of wood in a brilliant manner when given without a paint. • On the painted surface, varnish imparts a delicate brilliance. • Moreover, the resinous material dissolved in the varnish forms a thin film on the drying which protects the surface below from deterioration to moisture.
- 6. Ingredients of Varnish • The two essential component of varnish are a base or resinous substance and a solvent. The resin of varnish may be natural or artificial. Natural resin used in varnish are rosin, copal, shellac, amber, and dammar. Synthetic resin include phenyl, and vinyl resins. • The main solvent used in varnish are boiled linseed oil , turpentine, and methylated spirits. Water has also be used in some special varnishes.
- 9. Rosin
- 10. Copal
- 11. Shellac
- 12. Amber
- 13. Dammar
- 14. Solvent Used In Varnish
- 15. Type of Varnishes • Some common types of varnishes distinguished on the basis of the solvent of constituents are as follows: Oil Varnish • Those Varnish in which linseed oil has been used as a solvent form this group. The base material may be amber or copal. Although they dry slowly, they form a hard and durable film. Hence they are popular for use in external finish. They are quite resistant to weather changes.
- 16. Oil Varnish
- 17. Type of Varnishes Turpentine Varnish • These are made by dissolving gum, mastic or rosin in turpentine. They have the advantage that they dry quickly. At the same time, the film formed is neither much durable nor resistant to moisture. Hence they are used only in interior work.
- 19. Type of Varnishes Spirit Varnishes • They are commonly used varnish for furnitures. They consist of Shellac dissolved in methylated spirits. French Polish is a varnish belonging to this group. • Sometimes a small quantity of a pigment is also added to give a desired shade to the finish. The spirit varnish are also not much durable. They are also not resistant to weather changes. Hence these can be given only on wooden articles protected from rain, gases and light.
- 20. Spirit Varnishes
- 21. Type of Varnishes Japans • These are a class of varnishes that have asphalt as an Important ingredients. Asphalt is dissolved in a linseed oil in the presence of a volatile thinner. • JAPANS are applied mostly to metal surfaces. The surface is first- given a coat of JAPANS and then heated to baking temperature at 210 0 C for few hours. On Cooling, the paint forms a coating that is highly resistant to chemical corrosion.
- 22. Japans
- 23. References • Building Construction : Dr B.C. Punmia • Civil Engineering Material : Prof. Singh • Internet Web Sites
- 24. Thanks…