postcard.co.uk

Does anyone know of a detailed explanation of colour tinting methods employed by postcard photographers during the early years of the 20th Century - ie what material was used to achieve a colour impression on the images (composition of dyes), where was it commercially available from etc etc.

Am curious as I have many tinted examples from Sydney (Australia), some of these cards are very well executed, mainly by known photographers of the time.

Any ideas ?