Correcting defects and filling
Correcting defects and filling is now required. In the case of very small defects in glue joints a little hot hide glue will fill these in. Burning in with shellac stick of the correct color will fill larger errors. Shellac stick, spirit lamps and palate knives can be purchased from woodworking supply houses. Large defects may require the careful inlay of matching wood. When burning in heat the tool and clean it on a block of wood, then hold it over the spirit lamp flame until the shellac melts. Then with a flowing motion, apply the melted shellac into the defect. Wet your finger with saliva and quickly press the shellac into the void. Repeat, if necessary. Level the repair with a sharp chisel,scraper and sandpaper. Now damp off and filling if necessary is next. Filling - French polish can be used to fill the grain but fillers are usually used to save time. Plaster of Paris tinted to match is a traditional filler, first put a couple of coats of thin French polish on the wood. Next mix the plaster of Paris to the consistency of cream apply the plaster of Paris to the back of the guitar. Let it set for a little and wipe across the grain to level additional applications may be required. When the entire guitar is done take a little boiled linseed oil on a cloth and apply to the guitar. This takes the whiteness out of the Plaster of Paris. Rub with a soft cloth, sand lightly and you are ready to start polishing. Caution! Do not use a rag that has been used on tinted woods on light colored woods, use a new rag. Many ancient guitars will show the plaster of Paris filler. Pumice is put on the surface to be French polished and with the fad and shellac start working the pumice into the pours. A pounce bag is often used but filling can be done without. Use flour grade or fine pumice. Robert Ruck has recommended Elmers, Carpenters Interior Wood Filler tinting as necessary.