Title
A set of 24 touch needles
Caption
A set of 24 touch needles. These were made of the purest obtainable gold and each was alloyed with different known amounts of silver and copper, or of both. The sample of gold to be tested was rubbed on a hard dark stone, and the colour and thickness of the trace left was matched by one of the touch needs and the value of the sample obtained.
From "De re metallica", by Agricola, pseudonym of Georg Bauer (Basle, 1556).
Woodcut.
Date
1556
Credit line
Photo12/Ann Ronan Picture Library
Reference
ARP07111_009685P
License type
Rights managed
Available size
26,5Mb (1,4Mb) / 11,8in x 8,7in / 3543 x 2610 (300dpi)