Test Marks on Indian coins

At times it is necessary to check the hardness of the coin die, planchets and finished coins in order to ensure that they are neither too soft nor too hard. A die that is too soft will have a shorter life span and the one which is too hard will be brittle. 

Die Hardness Test Marks

After the mint prepares a coin die, they perform the Vickers hardness test on it. The machine has a probe (needle) that presses against the surface of the die. The depth to which the needle can penetrate under a specified pressure is measured on a dial and it gives an idea of surface hardness. The needle leaves a pyramidal mark on the die which then shows up on the coin. The mark slowly disappears as the die wears out, so coins struck later on in the life of the die may not show them. These marks maybe found on the obverse or reverse of the coin depending on where the test was performed. Some coins may have multiple test marks. Coins with these marks are neither 'rare' nor 'scarce'.

Image Courtesy -  Joseph Kunnappally 

Vickers Hardness Test

A needle leaves a pyramidal dent on the die surface
Image Courtesy : gordonengland

Privy Mark - A Misconception 

People often refer die hardness test marks as privy marks which is totally wrong. Privy mark is a small mark or difference in the design of a coin for the purpose of identifying the mint, Nowadays these are used as a design and marketing feature. Test and privy marks are entirely different. Test marks maybe collectible for some, but doesn't deserve to be categorized as "Rare" or "Scarce" neither they should be sold at premium prices.

        So what privy really is?

In the West, it notes issues for private enterprise. Mainly used as a design and marketing feature. For example the mint in Canada offers to put a company logo on silver rounds which is called a privy mark. It is applied to working dies and not the master die.

Privy mark on a Canadian coin.
Source - Royal Canadian Mint

Finally...

           Republic India coin collectors think that only Mumbai and Kolkata Govt mints have these so-called "Privy Marks" but example for Hyderabad and Noida mint coins with test mark(s) are known. Even examples for Indian Princely State and Pakistan test mark coins are known.

        Many British India coin books have attributed the “tiny diamond-shaped pyramid marks” appearing on the 2 annas, 1 anna and the ½ anna of 1946, as the identifying mint marks for the Lahore Mint in 1946. No evidence in support of this hypothesis is found, and rightly so as there is none. It is conjecture. Those marks are also "Test Marks". This will be discussed in the upcoming sequel.


Please note that marks similar to test marks are produced due to pitted dies and die chips. The way to differentiate is complex and will be discussed in the next post... Stay tuned..!
 

Special thanks to Joseph Kunnappally for the Photograph 


Continued on Test Marks Part 2