Test Marks Part 2

Continued from Test Marks on Indian coins


Hardness Testing is a basic procedure for coin minting. Not only India but many other countries test their dies and coins in order to ensure the life of dies and quality of minting.

Talking about US mints

The device used to measure the hardness in the US is the "Rockwell Hardness Tester". It measures the depth of penetration of the needle used in the test. A die that has had a Rockwell Test will leave a raised bump on the coin.
Unlike the Vickers Hardness Test, the Rockwell Hardness Test uses a needle which has a ball-like tip which creates a hemispherical indentation.

A Lincoln Cent showing Rockwell Test indentations.
Image Courtesy - Pete Apple

Did you know?
Indian coin blanks are also tested. Although this may not be done in mint itself (?). The companies which supply steel and coin blanks to Indian mints themselves perform this test (confirmed)  but no specimen with such mark is reported yet, maybe because these are destroyed by the companies after the test.

Differentiating Marks due to pitted dies and die chips

It is very important to note that in the Vickers Hardness Test the probe used gives a pyramidal shape mark which exactly measures 136°. This is the most important difference among an ordinary mark and mark due to a Vickers Hardness Test. Truly speaking it is next to impossible to measure such angles for an ordinary collector.

Image Courtesy -gordonengland

The pyramidal diamond indenter of a Vickers hardness tester.Image Courtesy -Wikipedia 

An indentation left in case-hardened steel after a Vickers hardness test.Image Courtesy - Wikipedia  

People often classify test marks too..! Elongated one... Flat one... etc etc which is totally WRONG..!

If the dots are too small, too numerous, or too scattered then the possibility of being evidence for some sort of controlled test greatly diminishes. The shape of the mark matters and is the critical factor in determining whether the mark is a test mark. Simply labeling a mark as a test mark won't work!

Some final words

I have noted the following after seeing many examples of the so-called "Privy-Test Marks of India"

1. When there are too many marks: Possibly it is due to pitted die. Same die is NOT tested repeatedly.
2.  Shape: Shape really plays a vital role here since it is the governing and differentiating factor for a real test mark. The shape is strictly pyramidal with an angle of 136°.
3. Size: Cannot be too small or too big but extremely minor variation in size may be seen.

The so-called "Elongated Marks". 
Image Courtesy - Ravi Jaiswal

The mark below "NA" of "FANAM" appears to be a test mark but the other three marks have different shapes, so the possibility is ruled out.
Image Courtesy - Joseph Kunnappally 

Similar Marks found on a coin from Pakistan. 
Image Courtesy - Joseph Kunnappally

A bit from history: The Vickers hardness test was developed in 1921. So marks on British India coins dating prior to 1930s are not due to Hardness testing. Surely some other technique might be used but not Vickers hardness test.

British India Coins

Image Courtesy - Joseph Kunnappally 

Pridmore states that the following mintage data for 1/2 Anna 1946- 

• Lahore mint produced 50 million, 
• Calcutta mint produced 75 million and 
• Bombay mint produced 49 million. 

However, both the Lahore mint and Calcutta mint did not have any mint mark to differentiate. British India books states that the only way to distinguish a 1946 Lahore mint coin from a Calcutta mint would be from the "die test marks". These test marks are supposed to be on Bombay and Lahore mint and not on Calcutta. 

But as discussed earlier in the previous post these are meant for checking hardness and has nothing to do with the identification of the mint.

To prove that the theory of identification is purely conjectured please see test marks on the following coins. 

Test Mark on Bombay mint coin

1/4 Rupee, Bombay, 1936.
Image Courtesy- Dinyar Madon

1/4 Rupee, Bombay, 1936.
Image Courtesy- Haresh Assumal

1/12 Anna, Bombay, 1939Image Courtesy - Joseph Kunnappally 

Test Mark on Calcutta mint coin

One Anna, Calcutta, 1943. 
Image Courtesy- Dinyar Madon

1/2 Anna, Calcutta, 1947.
Image Courtesy- Dinyar Madon

Test Mark on Lahore mint coin

Two Anna, Lahore, 1944.
Image Courtesy- Dinyar Madon

Conclusion 

The above images conclude that "Test Marks" are found even on Calcutta mint coins. Authors of British India Coinage have states that these marks are identification / differentiating marks which is wrong as these are marks due to hardness testing. Currently there is NO evident way to differentiate between 1946 Lahore mint 1/2, 1 and 2 Anna coins. Also, it is not possible that, one of the mint (Bombay and Lahore) is performing hardness testing whereas another (Calcutta) isn't. 

Currently, no 1946 ½ Anna can be attributed positively to the Lahore mint. 

The bigger question is 

"Did the Lahore mint produce coins in 1946?"

Another Mystery

Here is a coin, Rupees 2, 1992 Hyderabad mint.
Here you can see both types of Test Marks...

Image Courtesy - Ravi Jaiswal

The right one seems to be of a "Rockwell Hardness Test". Since it is raised, so it would have had to be done on the die. However, it is doubtful that this is a Rockwell Test, because the tip geometry does not match what it should be for a Rockwell Test. In US Mints, for example, the level of hardness of steel alloys for dies requires testing with the Rockwell C Scale. The requirements for using this scale with this level of hardness necessitate the use of a spheroconical diamond-tipped indenter. This means that the resulting indentation will have a different conformation than the hemispherical shape using the Rockwell 15T Scale which is applied to Cent blanks.

The left one seems to be a "Vickers Hardness Test", although the shape is not perfect.

Readers are requested to investigate this mysterious coin and share their views. I rest my pen for now..!

Special thanks to:-
Dinyar Madon for British India coin image.

Joseph Kunnappally for pictures.
Haresh Assumal 

Pete Apple for editing and writing assistance.

Ravi Jaiswal for the "Mysterious" coin images.


Please Refer http://conecaonline.org/content/RockwellHardnessTest.html for more on Rockwell Hardness Test Marks On Lincoln Cents.
Also, refer this discussion for more on BI coins http://www.worldofcoins.eu/forum/index.php?topic=24183.0