Oil and oil-varnish finishes

Unfortunately there is a great deal of mis-understanding and mis-information about varnish. The word has had a variety of meanings over time, and even today, it is used very imprecisely, especially on the containers of manufactured products. Do not rely on what the container calls the contents.

Some useful terminology 

  Varnish: is made by cooking one or more oils with certain natural or synthetic resins, which combine to then become a new substance. There 2 types of varnish; 

• spirit varnish, made by dissolving natural resins like sandarac, mastic and shellac, in alcohol or turpentine to facilitate application; (French polish)
• and oil Varnish, made by heating natural hard resins like copal or amber until they melt, then adding to a drying oil like linseed or tung oil to facilitate application.

  Today most varnishes are based on drying oils and use synthetic resins like phenolic or urethane. Generally sold as oil-based varnishes, applied with a brush, but by thinning to the consistency of milk, can become a wiping varnish. (Tru-oil)

  Wiping Varnish: Similar to oil varnishes, but thinner to facilitate application by a wiping pad. It cures by reacting with oxygen in the air, through a process called 'polymerisation'.

  Lacquer: another term that has been much abused and mis-used. It originated in the orient, as a deep, glossy finish, built up slowly in many, many layers. When replicated in the west it became known as 'Japanning'. Today lacquers refer to finishing products that dry by solvent evaporation. Mosty often they are designed to be sprayed, but can also be brushed or padded.

  Oil: is extracted from natural plant parts (notably seeds), fish and petroleum. It is usually mixed with other substances as a finish.

  Solvent: dissolves a cured finish, turning a solid into a liquid.

  Thinner: this just thins the liquid substance. It can not turn the solid back to a liquid.