what,s the difference between shellac and varnish?


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    4 Responses to “what,s the difference between shellac and varnish?”

    • ricknowspaint:

      hiya dennis…

      both varnish and shellac are hard drying, generally clear (although both can be pigmented) finishes used to protect, preserve and beautify wood….and that’s kinda where the similarities end.

      shellac describes a specific product, composed of a natural resin (excretions from the lac bug found in asia and india) usually dissolved in denatured alcohol (a blend of ethanol and methanol – other alcohols/glycols are commonly used to slow drying or affect application characteristics). shellac dries quickly and is very hard and brittle…much harder than lacquer, varnish, polyurethane, etc. (shellac is so hard, it was used to make old 45 & 78 rpm records)… a shellac film is also food safe and was once used as a coating on aspirin and other medicines to promote easier swallowing and slower dissolving.

      clear shellac (not pigmented opaque) is always gloss and is not always compatible with existing finishes. clear shellac is sold in "cuts"…a 3 pound "cut" is 3 pounds of shellac flakes dissolved per gallon of alcohol. while commercially packaged shellac is available in white (clear -water white) or orange (amber), the flakes are available through art supply houses in red, ruby, garnet, brown and other natural resin colors. like most varnishes, shellac finishes yellows over time.

      shellac is a non-reactive coating…in other words, the film forming (curing) process of shellac is simply solvent evaporation. once the solvent has evaporated, the shellac film has reached its maximum adhesion and hardness. because it is non-reactive, the finish will always soften or re-wet when exposed to alcohol.

      shellac is excellent for sealing wood, knot holes and water driven stains…it is also an excellent primer for plaster and drywall…it has outstanding adhesion to both slick and porous surfaces and may be applied to dusty, chalky surfaces with good results. because shellac is so hard and brittle, it is generally not recommended for exterior use (except for spot priming) or in areas of high moisture or humidity (in high moisture areas the wood will expand and contract at a rate greater than the shellac can – therefore cracking and peeling may occur)…

      varnish, on the other hand is a general term for just about any "reactive" clear finish. in a reactive coating, a chemical reaction takes place during and after the solvent evaporation to cure, or harden the finish. in the case of oil based (alkyd) varnishes the curing process relies on oxidation (reaction to oxygen molecules)…varnish resins may be alkyd, acrylic, polyurethane, vinyl, epoxy, and others…many times a combination of several different resins such as an acrylic modified polyurethane…these resins may be modified with different oils such as linseed, tung, tall or fish oil to achieve different finish results.

      while not as hard as shellac, varnishes are very durable coatings. they are more flexible and resilient than shellac so they can expand and contract as the wood does with less risk of cracking and peeling.

      varnish may be packaged for interior or exterior use… typically, interior use varnishes may be packaged in different sheens (gloss, satin, matte)…because of v.o.c. regulations, many solvent borne varnishes have been taken off the market (unfortunately)…polyurethane varnishes are very popular now as they are tough, durable coatings that are scuff, moisture and alcohol resistant. technological advances in arylics are making water-borne varnishes almost equal to their solvent counterparts in toughness and durability.

      which is better? …depends on the environment and application. shellac and varnish each has their own unique series of advantages and disadvantages. varnishes are generally regarded as being easier to apply and may be used in more environments than can shellac…shellac can be a little tricky to apply but is a beautiful finish with depth and color that varnish cannot duplicate…

      i don’t know if this info helps or confuses more, but now, at least you know some of the differences between the two.

      ric…

    • cocky:

      Varnish is a clear type liquid brushed onto timber to protect the surface.

      Shellac is a orange or white flake that has to be dissolved into metho before use,can be brushed or sprayed on.

      It is also used in the art of FRENCH polishing furniture.

    • Ler:

      Varnish is a finish made from wood resins. It tends to yellow over time.
      Shellac is made from excretions of the lac bug, found in parts of africa. It is particularly susceptible to alcohol.

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