Chapter 58
Emery in large grains may be broken by putting it on a cloth many times doubled, and hit it sideways with the hammer, when it will break up; then mix it little by little and it can be founded with ease; but if you hold it on the anvil you will never break it, when it is large.
Any one who grinds smalt should do it on plates of tempered steel with a cone shaped grinder; then put it in aqua fortis, which melts away the steel that may have been worked up and mixed with the smalt, and which makes it black; it then remains purified and clean; and if you grind it on porphyry the porphyry will work up and mix with the smalt and spoil it, and aqua fortis will never remove it because it cannot dissolve the porphyry.
If you want a fine blue colour dissolve the smalt made with tartar, and then remove the salt.
Vitrified bra.s.s makes a fine red.
729.
STUCCO.
Place stucco over the prominence of the..... which may be composed of Venus and Mercury, and lay it well over that prominence of the thickness of the side of a knife, made with the ruler and cover this with the bell of a still, and you will have again the moisture with which you applied the paste. The rest you may dry [Margin note: On stucco (729. 730).] [Footnote: In this pa.s.sage a few words have been written in a sort of cipher-that is to say backwards; as in l. 3 erenev for Venere, l. 4 oirucrem for Mercurio, l. 12 il orreve co ecarob for il everro (?) co borace. The meaning of the word before "di giesso" in l. 1 is unknown; and the sense, in which sagoma is used here and in other pa.s.sages is obscure.- Venere and Mercurio may mean 'marble' and 'lime', of which stucco is composed.
12. The meaning of orreve is unknown.]
well; afterwards fire it, and beat it or burnish it with a good burnisher, and make it thick towards the side.
STUCCO.
Powder... with borax and water
730.
STUCCO FOR MOULDING.
Take of b.u.t.ter 6 parts, of wax 2 parts, and as much fine flour as when put with these 2 things melted, will make them as firm as wax or modelling clay.
GLUE.
Take mastic, distilled turpentine and white lead.
On bronze casting generally (731-740).
731.
TO CAST.
Tartar burnt and powdered with plaster and cast cause the plaster to hold together when it is mixed up again; and then it will dissolve in water.
732.
TO CAST BRONZE IN PLASTER.
Take to every 2 cups of plaster 1 of ox-horns burnt, mix them together and make your cast with it.
733.
When you want to take a cast in wax, burn the sc.u.m with a candle, and the cast will come out without bubbles.
734.
2 ounces of plaster to a pound of metal;- walnut, which makes it like the curve.
[Footnote: The second part of this is quite obscure.]
735.
[Dried earth 16 pounds, 100 pounds of metal wet clay 20,-of wet 100,-half,- which increases 4 Ibs. of water,-1 of wax, 1 Ib. of metal, a little less,-the sc.r.a.pings of linen with earth, measure for measure.] [Footnote: The translation is given literally, but the meaning is quite obscure.]
736.
Such as the mould is, so will the cast be.
737.
HOW CASTS OUGHT TO BE POLISHED.
Make a bunch of iron wire as thick as thread, and scrub them with [this and] water; hold a bowl underneath that it may not make a mud below.
HOW TO REMOVE THE ROUGH EDGES FROM BRONZE.
Make an iron rod, after the manner of a large chisel, and with this rub over those seams on the bronze which remain on the casts of the guns, and which are caused by the joins in the mould; but make the tool heavy enough, and let the strokes be long and broad.
TO FACILITATE MELTING.
First alloy part of the metal in the crucible, then put it in the furnace, and this being in a molten state will a.s.sist in beginning to melt the copper.
TO PREVENT THE COPPER COOLING IN THE FURNACE.
When the copper cools in the furnace, be ready, as soon as you perceive it, to cut it with a long stick while it is still in a paste; or if it is quite cold cut it as lead is cut with broad and large chisels.
IF YOU HAVE TO MAKE A LARGE CAST.
If you have to make a cast of a hundred thousand pounds do it with two furnaces and with 2000 pounds in each, or as much as 3000 pounds at most.
738.
HOW TO PROCEED TO BREAK A LARGE Ma.s.s OF BRONZE.
If you want to break up a large ma.s.s of bronze, first suspend it, and then make round it a wall on the four sides, like a trough of bricks, and make a great fire therein. When it is quite red hot give it a blow with a heavy weight raised above it, and with great force.
739.
TO COMBINE LEAD WITH OTHER METAL.
If you wish for economy in combining lead with the metal in order to lessen the amount of tin which is necessary in the metal, first alloy the lead with the tin and then add the molten copper.
How TO MELT [METAL] IN A FURNACE.