The Brass industry
We have already seen that much of the copper mined by the ancients was used to make Bronze. This metal was harder than copper and made tools and decorations which were longer lasting.
For much the same reasons much of the copper mined in the 17th and 18th centuries were used to make brass. Initially this brass was made by the cementation process using the zinc containing ore called calamine. The method had been known to Georgia Agricola and was mentioned in his De Re Metallica , published in 1556. Agricola maintains that the method was known to the Greeks and Romans when the ore was called lapis calaminaris.
Preparation of Brass using the calamine cementation process.
In the 16th and 17th centuries calamine was mined in Somerset and Nottinghamshire by the Mineral and Battery works. The methods used to mine the ore were described in 1684.
A deep trench was dug across the area where they expected to find the ore. The colour of the earth containing calamine was described as being a yellow grit. This material was taken to the surface where it was cleaned.
A small enclosure was made of boards or turf’s. The raw ore and earth was shovelled into the enclosure. A stream was then diverted through the enclosure and the earthy material washed away. The heavier ores remained. The larger parts were removed by hand while the small material was put into sieves and washed again. This resulted in heavy lead ores going to the bottom of the sieve the calamine ores to the middle and the small light stones to the surface. The calamine was recovered and spread out onto a board and foreign material picked out by hand.
The ore was then calcined in a large oven for 4 or 5 hours. The oven was divided into two parts, the ore was placed in the second part and a fire was set in the first. The flames from the first partition passed over the top of the partition wall and were allowed to burn the ore. The baked ore was taken out of the oven, spread out and then beaten to a powder with long iron hammers. It was this powdered ore which was used to combine with copper to make brass.
The calamine powder was mixed with small coal in the ratio of one calamine to two coal dust. When well mixed a small amount of water or urine was added and a thick paste allowed to develop over 1 hour. This mixture was then further mixed with salt and stirred.
The next steps were described by Pettus in1670:-
” In one of these ovens they set 8 pots at once and let them be warm and hot, and when they are so, they take them out quickly and put 46 pound of the calamaris mixture in the 8 pots. In each pot they then lay 8 pound of small broken copper pieces and set them it pots again. The pots stand for 9 hours in a great heat. And in this hour are taken one heap and a half of coals, and when the coals are burnt out they stir the stuff in the pot with an iron. After a further time, the pots are taken out of the oven and all the brass poured into one “king pot”. When the whole mixture was ready the dross was skimmed off and the brass was poured between two stone moulds. When cooled a plate of about 70-pound weight was obtained.
This method of making brass from calamine was carried on until as least as late as 1858. However, during this time some other methods were also discovered.
In 1738 the Champions of Bristol developed a method of extraction zinc metal from the calamine ore. By 1758 he had shown how this metal could then be reacted directly with copper to make a better quality brass.
There were a number of grades of brass which were made for different uses:-
Name % copper % Zinc % Others
German Brass 49.5 50.5
Wire brass 65.4 36.6
Common Brass 66.6 33.4
Sheet brass 74.6 25.4
Bath Metal 82.9 17.1
Cock metal 88 2 10 Tin
Whistle brass 80 2 18 Tin
Strerro metal 55 42 5 Iron
The manufacture of articles from Brass and Copper
There were two main traditional processes employed in the manufacture of Brass articles which dated back to Elizabethan times.
The first was the “battery works” which involved the use of hammers of various weight of up to 500 pounds being driven by water power. A Brass ingot of 70 pounds would be hammered into a plate of the correct thickness. The plate was then cut into circular shapes and four or five of these hammered together. These plates were then raised up round into hollow shapes using a hammer and anvil.
There was a great art in using the correct hammer and amount of heat to ensure that the plates did not stick to each other during the battery process. In addition, the battery works had to be situated close to a good source of water to run the water wheels which operated the hammers. This dependence on water power remained until the development of steam power.
Towards the end of the 17th century rolling mills came to be used instead of battery mills for flattening brass and copper ingots. These sheets were used to make coinage. The battery mill hammer was still needed to raise brass into pots and pans.
The second traditional brass process was wire drawing. Prior to the adoption of water power, wire was drawn by hand. This involved men sitting in swings opposite each other with a thin sheet of brass attached to a girdle fastened around their waist. The men pushed against a stump with their feet and swung away from each other thereby pulling the brass until it was stretched into wire.
When water power became available brass plates weighing 70 pounds were cut into 7 or 8 strips and these strips stretched on the rolling mill to the desired thickness. The metal was occasionally annealed to keep in pliable. The stripes were next cut into many long threads and were drawn through holes in iron to such sizes as were required.
This wire was used to make pins and also the combs needed to card wool.
Around 1700 the casting process for brass was developed and was beginning to displace the battery method for the manufacture of smell articles. Patterns of articles were made of wood. A bottomless iron box was filled with a layer of special damp casting sand. The wooden pattern was then pushed halfway into the sand. The surrounding sand was well rammed to make of good impression. The surface of the sand was then dusted over with charcoal to form a “parting surface”. A second topless box was then placed upon the first and also filled with sand. this was rammed home to give a good impression of the top half of the pattern.
Moulding boards were then placed over the top and bottom halves of the box and the two halves separated. The pattern was removed and the sand dried with a blowtorch. If a hollow casting was to be made, special cores of the correct shape were added to the impression in the sand. The boxes were then placed back together and molten metal poured into them. After cooling the boxes were opened again, the sand removed and the articles hand finished.
Towards the end of the 18th century a new method of producing brass articles called stamping began to be developed. In 1769 a John Pickering was granted a patent, No 920 , to stamp certain articles from sheet metal. This process had become available due to the advent of steam driven machinery and rolling mills to produce sheet metal. Pickering used his invention to make ornaments for coaches and carriages and also coffin furniture.
To achieve this, he invented a machine consisting of a moving weight or hammer, faced with soft metal, which was to move between two rods. The hammer was allowed to fall on the sheet metal beneath which was placed a die. The weight of the hammer and the die produced a pattern in the metal which could then be cut out and hand finished. It was not long before further inventions were added which allowed both sides of the sheet to be stamped and even stamped into a shape with a press.
Saucepans and frying pans, which had previously been made by the battery process, could not be made more easily using the stamp process. In addition, small articles such as thimbles, buttons and buckles could be easily produced in much large quantities and much more consistently.
In 1779 William Bell invented a way of “affixing impressions from dies upon metals by means of rolling cylinders on which dies had been engraved. These rolling presses lead to even more economies and increase in the number of household articles made from Brass and copper.
Around 1790 Williams Collins and Charles Wyatte of Birmingham took out Patent No 1739 ” a new article of trade and commerce being an improvement of copper sheets or plates and brass sheets or plates, by covering and combining them with a metallic or semi metallic substance, which covering will prevent all noxious effects from these metals when used for culinary purposes or for containing or carrying water”
Hence the process of plating brass was started. This process was use on household equipment to reduce the incidence of metal poisoning which was becoming a problem. In addition, it provided a new process to the button and buckle industry.