1 Packet, Cochenilla precipd. by tin ) Tied together with string
This item is part of the contents of the workshop that Scottish engineer James Watt developed at his home, Heathfield, at Handsworth, Birmingham, from c.1795 through to his death in 1819. Although Watt is best known for his work on the steam engine, his workshop contains a wide variety of objects from many different projects, from chemistry to sculpture-copying.
The description of the item was written by Edward Collins, the land agent responsible for Heathfield when the workshop was given to the Science Museum in 1924. Collins could not always identify what he was looking at, but always described what he saw clearly. This has allowed his descriptions to form the basis of subsequent research.
This substance is associated both with dyeing (cochinella producing a rich red colour) and, more probably, with testing the strength of the bleach produced using chlorine in Watt's new bleaching process.
It is part of a broad group of substances which Watt collected and stored in his workshop. They comprise different quantities, each individually placed in a packet or box, and usually labelled in Watt’s hand. The substances reflect Watt’s very wide chemical interests, from making the ink for his letter-copying presses, to ceramic glazes and dyestuffs (Turkey red, for example), then latterly chemical compositions to protect the surfaces of plaster casts while they were used in the workshop’s sculpture copying machines, and even the ingredients of the plaster casts themselves. It is also possible that Watt kept some substances for their medicinal qualities, relating both to his interest in pneumatic medicine, and the need to keep his family in good health.