av Raymund » 6 februari 2008, 21:49
Så här står det i Theophilus mer ordagrannt:
<i>"The Gluten [Called] Varnish
Put some linseed oil into a small new pot and add some very finely ground resin, which is called fornis, and which looks like very clear frankincense except that when it is broken up it has a higher luster. After putting it on the fire, cook it carefully, without letting it boil, until a third of it has evaporated. Beware of flame, because the varnish is extremely dangerous and, if it should catch fire, difficult to extinguish. Every painting that is coated with this gluten is made bright, beautiful, and completely lasting.
Another method.
Set up four stones which can withstand fire without spalling, and place a raw pot upon them. In the pot put some of the afore-mentioned resin, fornis, which is called glassa in Roman. Over the mouth of this pot place a smaller one with a little hole in the bottom. Smear some paste around it so that no air can escape between the two pots. Then build a fire carefully beneath it until the resin melts. You should also have a thin iron rod fitted into a handle, with which you can stir the resin and feel when it becomes completely liquid. You should also have a third pot on the fire close by, with hot linseed oil in it. When the resin is thoroughly liquid so that, when you take out the iron rod, a sort of thread is trailed behind it, pour the hot oil into it, stir with the rod, and cook them together without letting them boil. Occasionally take out the rod and smear a little on a piece of wood or stone to test its consistency. Take care that there are two parts of oil and a third part of resin by weight. When you have cooked it carefully to your satisfaction, take it off the fire, uncover it, and let it cool."</i>
Det är alltså en harts/linoljeblandning som värms. Tyvär så kan man inte riktigt lista ut vilka typer av harts som avses.
(Theophilus On Divers Arts är daterad till ca 1122.)
/R