VARNISH :
Varnish is a solution of resins or resinous substances like shellac, cobalt in oil, turpentine or alcohol.
NECESSITY
i. To provide a brilliant and decorative covering on wooden surface.
ii. To protect the painted surface from the atmospheric action.
iii. To protect unpainted wooden surface of doors, win- dows, floors, roof trusses etc., from atmospheric action.
Ingredients of Varnishes
1. Resin
2. Solvent
3. Drier
Types of Varnish
1. OIL VARNISH: The varnish which is prepared using linseed oil as solvent is known as oil varnish. Oil varnish is used both for interior as well as exte- rior works.
2. SPIRIT VARNISH: The varnish which is prepared using methylated spirits of wine as solvent is known as sprit varnish. It dries quickly. It is generally applied on the wooden surfaces. It is also known as ‘French Polish’.
3. TURPENTINE VARNISH: These varnishes consist of soft resin like gum, dammer, mastic and resin dis- solved in the best turpentine oil. This vamish dries quickly, but is not so durable.
4. WATER VARNISH: These varnishes are formed by dissolving shellac in hot water using enough quanti- ty of ammonia, borax, potash (or) soda. Water var- nishes are used for varnishing wall papers, maps, pictures, etc.
Properties of Varnish
i. Gives brightness to the surface and a glossy look.
ii. Varnish should not be allowed to dry quickly.
iii. After varnish is applied the wood becomes hard.
iv. Surface of the varnish applied will not allow the wood to shrink.
Uses of Varnishes
i. It gives permanent glossy film.
ii. It is cheap when compared to paint.
iii. It protects the surface from weathering
Varnishing on Wood Work
PREPARATION OF THE SURFACE: Surface to be varnished must be made perfectly smooth with sand paper.
REMOVING KNOTS: Shellac and naptha are added with varnish and it is applied on the knots and they are removed
METHOD OF VARNISHING: Varnish should be applied uniformly in very thin coats and sprinkling at angles and comers. The second coat should be applied only after the first coat becomes hard. The brush used for var- nishing should be of fine haired type and not ordinary paintbrush.
