A sealer is a substance used to protect a surface from oxidation, natural deterioration and physical abuse. Numerous types of sealers are found commercially, each providing a specific solution for a sealers needs.

The term ‘varnish’ has become a common word referring to a general sealer. There are considerable differences between varnishes and other sealers and for accurate results the proper terminologies should be used.

Varnish:

Varnish typically is petroleum based or tree sap based clear sealer. Varying degrees of sheens are found, from matt (flat), to eggshell, satin (pearl), semi-gloss and gloss (high gloss). Most commonly used for furniture, floors, objects, and the ship building industries. Varnish comes in 2 basic categories, oil based and water based. Each category has different types, for example, Spar varnish, Damar varnish, re-touch varnish.

Oil: A petroleum based product that is very durable. It has a longer drying time than it's acrylic counterparts, and some forms may slightly yellow over time, and when exposed to natural light. Recommended for commercial use and any areas that have high traffic zones.
Solvent: Mineral spirits, turpentine 

Acrylic: Acrylic varnishes have now greatly supplemented its longer drying oil based counterparts. The quick application time, fast drying, durability and easy clean up make acrylic varnishes ideal for interior uses. Acrylic varnishes remain clear after drying and are commonly used for floor sealing, objects and furniture.
Solvent: water

Never shake varnish. Only stir it to mix properly. Shaking will create air bubbles in the varnish. This can result in poor application and an irregular finished surface.

A few excellent varnish products for floors, furniture and objects are latex varnish , a latex-water based sealer, and oil varnish , an oil based sealant.

Shellac:

Shellac is produced from the secretions of a bug, deposited on branches of trees in India. Shellac can be diluted with denatured alcohol to make the shellac workable, or to dissolve and remove shellac. Typically used on furniture, shellac can be used as a fast drying sealer. French Polish and simulated lacquer techniques employ the use of shellac as a sealer.
Solvent: denatured Alcohol

White pigmented shellac: Products such as BIN is commercially available. Essentially a combination of shellac, denatured alcohol and titanium dioxide, pigmented shellac makes an  excellent fast drying sealer, especially good for covering water spots, bare wood that has sap exposure and surfaces that may have slight grease or wax build up.
Solvent: denatured alcohol

Warning: Shellac is highly toxic. It has a strong odor and should always be used in a well-ventilated area. Respirators and protective gear is recommended with the use of any shellac product.

Lacquer:

Used commonly in the industrial environment, particularly in the automotive industry and furniture production. Lacquer is well suited for mass production processes. Lacquers are typically made of nitro-cellulose, cellulose acetate, and other forms of cellulose. Lacquers dissolve in special solvents such as acetone, ethyl acetate, butyl alcohol, etc. 
Lacquers should not be used in Fine Art painting as its level of permanence is low. Pigmented lacquers display signs of deterioration in as little as 10 years, from exposure to daylight.
Lacquers are often used because of their fast drying time.

Natural lacquer (Oriental): Exude natural from trees in a liquid state. Natural lacquer is used for local production and is not exported.

Solvent: Lacquer thinner

Warning: Lacquer is highly toxic. It has a strong odor and should always be used in a well-ventilated area. Respirators and protective gear is recommended with the use of any lacquer product.

Urethane, Polyurethane and Varathane:

These are derivatives of varnish. Each maintains a particular property that makes it suited for specific functions. Primarily due to hardness, elasticity, and yellowing qualities over a period of time and exposure to light. Floors, furniture and objects are ideally suited for urethane sealers. Surfaces requiring a barrier of protection to oxygen, water or moisture, and physical damage over the course of use are candidates for protection of a varnish product.
Solvent: Mineral Spirits, turpentine, turpenoid.

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