146 
DR. C. B. PLOWRIGHT ON WOAD AS A BLUE DTE. 
110° to 140° F., not going above 150° or letting it fall below 100°. 
In about 13 — 14 hours bubbles of gas begin to rise; a very small 
quantity of slaked lime should now be added ; and in a few hours 
woollen articles allowed to remain in it for an hour or two change 
from yellow to blue as they are taken out and exposed to the air. 
When the vat is in full working order the liquid is of an olive- 
brown colour, on the surface of which darker veins appear which 
change their position, slowly moving, appearing and disappearing 
spontaneously. The froth which at this time gathers on the surface 
of the vat is blue from the indigo precipitated by contact with the 
atmosphere. This constitutes the cceruleum spuinam Ruellius* 
speaks of as being dried and sold to the painters. It was also the 
“ flowers of the Woad ” which the dyers of Coventry f were accused 
of skimming off the Woad vats in which they dyed their customers’ 
goods and added to those vats in which they dyed their own. It 
is interesting to notice that if a skein of wool be suspended in a 
small experimental vat in good working order, that it is the upper 
part of the skein nearest the surface which takes the deepest 
colour, and next to it, as one would have imagined, the lower part 
nearest the sediment at the bottom. This blue scum was the 
probable source, not only of the Woad blue which Pliny J speaks of 
as being used in his time to stain chalk with for the adulteration 
of indigo, but also of the “ ancient Briton ” pigment of which we 
hear so much and know so little. Caesar § and Pomponius Mela|| 
speak of our ancestors staining their bodies blue ; it is difficult to 
understand how they could dye their skin blue, but is easy to see 
how they could have smeared themselves with Woad blue mixed 
with oil or grease. Herodian,1T however, throws a little more light 
on the subject when he tells us that “they mark their bodies with 
various figures of all kinds of animals, which is the reason they 
wear no clothes, for fear of hiding these figures.” The use of 
indigo for tattooing is still common among our soldiers and sailors. 
In conclusion I must express my thanks to Mr. C. G. Barrett, of 
Gaywood, for his valuable assistance and advice in conducting the 
numerous experiments with Woad vats which have been made. 
# Ruellius, loc. cit. ante. 
t Petitions to Parliament, III. Henry V. (1415), for which reference 
I am indebted to Mr. Walter Rye. 
% Pliny, Nat. Hist. xxxv. 6. § Caesar, ‘De Bello Gallico,’ v. 14. 
|| Pomponius Mela, ii. 1. *|[ Herodian, iii. 47. 
