[Fol. 173, v.]
For to make reed wex. Take a pound of whight wex, and throwe therinne a quartroun of terbentyne, and melte hem two togidere; and if thou wolt asaye it if it be weel gummed, caste a litil in coold watir, and thanne asaye it if it be tendre, and if it be tendre it is weel gummed. Thanne loke thou have redy oz. 1 of vermyloun, smal grounde, al so smal as ony poudre, and whanne thi wex and thi terbentyne is hoot molten, anoon rijt throwe yn thi poudre of thi vermeloun, and sette it adoun of the fier, and styre it weel, and meynge it weel togidere til it be coold, and thanne thou hast good reed wex y-mad.
For to make grene wex. Take lj. 1 of whight wex, and quart 1. of terbentyne, and medle hem togidere, and asaye if it be weel gummed as thou haddist the rede wex right in the same maner, and thanne take an ounce of vertegrece smal broken, and y-grounden upon a marbil stoon, and throwe it in the matere, and styre it til it be coold, and thanne thu hast good grene wex.
Quartroun: quarter of a pound
Terbentyne is not spirit of turpentine, but terebinth resin. Dammar resin is used similarly in modern encaustic painting, mixed with beeswax to add gloss, toughness and hardness, and to raise the melting point.
I have been unable to obtain terebinth resin, but I have experimented with mastic resin. Terebinth is produced by the terebinth tree, Pistacia terebinthus and Pistacia palaestina. Mastic is produced by the mastic tree, Pistacia lentiscus. They are members of the same genus, and so closely related that Pistacia saportae is believed to be a hybrid between P. terebinthus and P. lentiscus.
Mastic and dammar have similar properties when used as a varnish or to temper wax, but less dammar needs to be added to the beeswax for the same hardness, and mastic is much more expensive.
I experimented with a mixture of mastic and beeswax, in the proportion of the above recipe. Mastic has a higher melting point than beeswax, so I melted it first on a pan with a digital thermometer, and then mixed in beeswax. The result, as expected, was harder than untempered beeswax, with a higher melting point. It seemed somewhat softer than a typical recipe for contemporary encaustic medium which uses one part dammar resin to six parts beeswax, but a dammar based recipe could achieve similar hardness by adding more beeswax.
Wax for wax tablets would probably use a higher proportion of beeswax than sealing wax. Artists' encaustic medium would serve well as sealing wax, but I believe from my experiments that three parts beeswax mixed with two parts encaustic medium would serve better for a writing tablet.
Encaustic medium using dammar resin is available, with our without pigment, from any well equipped art supply store. You can make it yourself, and if you want it in quantity you will spend less on materials. The process is tricky, however, since the temperature at which dammar resin dissolves is awkwardly close to the temperature beeswax starts to smoke. And smoking beeswax is a bad thing.
For small projects, I believe prepared encaustic medium is a better starting point.
British Museum MS. Sloane, No. 73 in British Archaeological Association. 1845. The Journal of the British
Archaeological Association: for the encouragement and prosecution of
researches into the arts and monuments of the early and middle ages. London: British Archaeological Association. Vol. 1 p. 152
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