One very characteristic element in early guitars is the use of black and colored mastic for inlays. Like in the border around the sound hole or intricate patterns on the soundboard.
A little graft is made and cut pieces of bone, ivory or sometimes mother of pearl are added.
Then the space around it is filled with a paste made of pigment and bone or hide glue.
Often they used soot or charcoal for the black pigment. Because I like to find creative ways to deal with waste, I make this pigment myself. When you use a rag to put on a drying oil finish, don’t throw it in the dumpster afterwards. There is a chance that it may combust and set the thing on fire… Drying oils like linseed, tung or walnut oil bind with the oxygen in the air. It’s an exothermic reaction, like rusting or fire. When the temperature becomes too high the rags may catch fire…
To avoid this I keep used rags in an airtight paint can. Once it is full the rags are taken outside and burned. Because of the oil it gives off a very sooty smoke, and the cloth is charred but stays quite firm.
After the fire is out the remains are ground up, resulting in the black pigment.
The pigment is mixed with animal glue (75% bone and 25% hide glue) and put in the graft.
After it has hardened the inlay can be scraped clean…
Instead of black pigment I used mahogany dust for the inlay on the large guitar. It’s a bit of reddish-brown.
To learn more about the guitars by Stradivari, read my American Lutherie article here…