‘Now,’ says Mathesius, ‘we come to the German glass-houses. Some have their own sand, others pound white quartz and pebbles. They make use of the ashes of oak, maple, beech, and pine; the ashes of the fir and of the willow turn out good work, but from their fatty nature yield glass that is not so white. Native salt is added also to the sand and ashes, but the Polish rock-salt is more advantageous. Many buy up broken glass and make with it the best work.’[196] If you wish, continues Mathesius, to obtain white and pure glass, it is essential to use only well dried wood, for green wood makes the glass opaque and blackish. The metal should be cooled more than once and remelted, the glass-gall being carefully skimmed off each time. If you propose to make fair and pure glass, ‘neither bubbly, feathery, cloudy, dull, stony, or gritty,’ prepare your frit carefully by rabbling and turning over the mixture of sand, potash, and salt on the floor of the first furnace, in the same way as metallic ores are treated ‘when they are roasted by the valuable new process.’ (Whatever this may have been, it was an illustration that would appeal to his audience of miners.) When the mixture begins to sinter together, the stuff should be shovelled into cold water. The frit thus prepared is then placed in the melting-pots and gradually heated. There then follows a careful account of the various processes involved in the blowing and shaping of the vessel: of this I will only remark that there is no mention in it of the use of the shears for trimming the rough edges of the glass—technically an important point. ENAMELLING ON GERMAN GLASS We are now able to form some idea of the processes by which glass was made in Central Germany about the middle of the sixteenth century, and when we come to examine the glass itself by the aid of extant examples, it will be found that this is indeed the date from which the start must be made, for there are few pieces in our collections that can claim a greater antiquity.