French Polish

 Many of the old Italian mandolins were polished with shellac, though many later instruments, from perhaps the 1920s were also varnished. To restore a beautiful Italian bowlback to it's former glory, I feel it only right to French polish it. Thus this section is about French polishing... and yes, it has taken me some time to get it all together, as there is both a lot of mystique, a lot of mis-information, and for me anyway, a lot of new knowledge involved, though the actual process itself is relatively straight forward.

    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. e.g. (Tru-oil)

About Shellac

   How do I buy shellac? Grades include seedlac; buttonlac; *1 orange; Kusmi blonde; and bleached white.It is sold in flake or liquid form. For luthiers, the problems are compounded by the fact that, shellac has varied commercial applications. For instrument finishes, you are interested in liquid or dry flake shellac.

   What is the shelf-life of shellac?

•    Liquid Shellac: The liquid is pre-mixed, often as a 3 lb cut. Liquid shellac starts to lose its effectiveness as soon as it is dissolved. It begins to lose its resistence to water and its ability to cure hard. Commercial liquid shellac may have other agents added to slow down drying time or aid application.... none of these are necessary or helpful when French polishing.... AND you never know how long it has been on the shelf!!
•    Dry Shellac: has a much longer shelf life, but still degrades over time, as it is a complex compound of organic acids. Over time it will form molecules that will not dissolve in alcohol. If you are left with a jelly-like sludge in the bottom of the jar, even after several days, it is past its sell-by-date. (not to be confused with wax at the bottom in un-bleached varieties)
•    I would always advise flakes... as flakes, you can mix up as much or as little as you need.

   Are there different types of shellac flake? Yes. Shellac flakes come in a variety of forms, though each manufacturer seems to have their own names for each?!

• Orange shellac; the natural shellac resin (also called amber, garnet or button) is this colour, adds warnth to dark wood, will darken light woods, but without obscuring the grain. It will also contain about 5% natural wax.
• White shellac; is bleached so much lighter, and will darken light woods much less.
• Dyed Shellac; you can add alcohol-soluble dyes to shellac in small quantities to colour it.
• 'Blonde' shellac; is clear and has been de-waxed.

   Why de-wax shellac? Natural shellac comes with about 5% wax. This will lower its resistance to water; reduce its transparency; and prevent good bonding with non-evaporative finishes such as varnish. It can be removed after application, (see French polishing sequence) or before (by letting the solution stand for a few days, and siphoning off the solution, as the wax settles to the bottom.

   Can I de-wax myself if I buy un-bleached shellac? Yes. Either by siphoning off the solution, leaving the wax at the bottom, or by repeated filtering with a fine muslin or cheesecloth.

   How do I know if my jar of shellac is still ok? To test if it is still good, place a drop of shellac on to a glass surface and wait. Afetr aboiut 15 minutes, it should be dry to the touch.Leave it overnight. The following day scratch the surface, if it is still gummy, then it has gone off and should be thrown out.

   How do I apply shellac? Shellac can be applied by brush, spraying or rubbing once it is dissolved in alcohol. Brushing and spraying can apply shellac quite thickly, but may need sanding in between coats. Rubbing (the process of French polishing) applies it very thinly, it doesn't need sanding between coats, but takes a long time to build up thickness. Rubbing can also be used as a method of 'finishing' shellac applied with spray or brush.

   What does '3 lb cut' mean? 'Cut' is a term used to measure the strength of a mix of shellac; specifically, how many lbs of shellac are dissolved in 1 gallon of alcohol. The higher the number, the thicker the shellac.

   Advantages of Shellac? 

• as a finish it lasts a long time.
• it is easily repaired in the event of damage.
• it is safe and non-toxic.
• It adheres to most finishes, and they adhere to it, so it is adeal for repairing other finishes.
• its solvent is much less pollutuing than solvents of other finishes.

   Disadvantages of Shellac?

• it is fairly resistant to humidity, but may be caused to 'blush'.
• it is not resistant to water.
• alcohol will easily damage the surface.
• heat will often soften the shellac.
• it is susceptible to alkali damage.

Problems with Shellac...

• good surface preparation.
• not too thick a cut (2 lb is fine).
• use 'blonde' shellac.
• make sure your environment is as dust free as possible.
• carry out French polishing in a warm, dry, dust-free room.

   most of the problems can be easily remedied by sanding out and starting again, but I will list some of the more common below and their causes.