The book
Tin 'Hat' and Animal Money by Shaw and Kasim published in 1970 by Muzium Negara, Kuala Lumpur, Malaysia is a useful reference on the subject. This 17-page book, excluding 9 pages of exhibition plates focuses more on Tin 'Hat' (Pagodas and Pyramids) money but provides a brief but good background information on the development of animal money.
Five out of nine exhibition plates included in the book presented items of animal money (animal currency) in the collection of Muzium Negara, Kuala Lumpur, Malaysia. Many of these items were subsequently included by Saran Singh in
The Encyclopaedia of the Coins of Malaysia, Singapore and Brunei - 1400 - 1967 that was first published in 1986.
The book touches on the tin mining activities carried on in the Malay Peninsula and how superstition govern the operation,
the working of a Malay mine belonged rather to the province of magic than of mechanics (Winstedt 1909, pp. 28). The minting of tin ingots in the shapes of animal and insects is a fascinating development of the tin currency that is least understood. The book suggested two hypothesis with regards to the purpose of the tin animal and insect ingots. First, for magical ceremonies (possibly connected with tin mining activities) and second, used as weights (to check correctness of the standard tin ingots). Shaw and Kassim referred to Klinkert's
Malay-Dutch Dictionary (p. 129) where
Boewaja (
Buaya) the crocodile was the name of a tin money in Selangor that had the value of 20
duit (doits) as evidence that tin animals indeed passed as a currency in the past.