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schema:abstract "25 - Thrice Baked Copper Scale for Glass ColoursPut the above mentioned red copper scale into an oven, or better still in the annealing chamber of the furnace near the 'eye', on terracotta tiles or even on terracotta oven-pans. Leave it to calcine continuously for 4 days; it will become a black powder that lumps together. This must be freshly ground and sifted with a fine sieve and returned to calcine as before in the annealing chamber of the furnace, leaving it 4 or 5 days. At this point, it will not stick together any more and it will no Ionger be black but grey, and turn to powder. This is called 'thrice baked' copper scale with which are made aquamarine, emerald green, the Arabic colour called turquoise, which is a very serene sky color, and many others. However, you must take care in the third calcination that it is not done too much, or too little, because in either case it will not color the glass well. The sign of perfect calcination is to sprinkle some of it over crucibles of clarified glass, even in larger crucibles; it will swell and boil suddenly. lf it does not give this sign then it is no good, nor well calcined, so you must be sure that it shows this sign to have it perfect." ;
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schema:description "Ramina di tre cotte per i colori di vetro. Cap. 25., L´arte vetraria distinta in sette libri del R.P. Antonio Neri Fiorentino: ne quali si scoprono, effetti maravigliosi; & s´insegnano segreti bellissimi, del vetro nel fuoco & altre cose curiose., Antonio Neri" ;
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