What was encaustic

"Now wax is made white after this manner. Having cut white and clean wax into small pieces, cast it into a new vessel, and pouring thereupon as much sea-water, taken out of the deep, as shall be sufficient, boil it, sprinkling a little nitrum upon it. And when it shall have boiled twice or thrice, taking off the vessel and letting it cool, take out the cake, and scraping off the filth, if there be any about it, seeth it a second time, putting other sea-water to it; and when the wax shall have sod again, as has been formerly shown, take away the vessel from the fire, and taking the bottom of a little new vessel first moistened with cold water, let it down gently into the wax, dipping it in a little with a soft touch, that a little of it may be taken and that it may be concreted together with itself. Having taken it up, pull off the first cake and again let down the bottom, cooling it in water anew, and do this so long till you have taken up all the wax. Then piercing these little cakes with a linen thread, hang them up at some distance of each other, and in the day-time setting them in the sun, sprinkle them every now and then with water, and at night set them under the moon till they become perfectly white. But if any would make it extraordinarily white, let him work the other things in like manner, but let him seeth it often. But some instead of sea-water taken out of the deep, boil it in the aforesaid manner once or twice in very sharp brine, then afterward they take it out in a thin and round bottle having an handle, afterwards laying the little round cakes upon thick grass, they sun them until at last it becomes wonderfully white. But they do advise to set about this work in the spring when the sun both remits of its vehemency and yields dew so that it shall not melt". Dioscorides. De materia medica, 2, 105.