How Were The Canadian Olympic Stamps Of 1974 Produced?

The Canadian archive tells me that these were produced using a new form of steel engraving that showed one image when looked at normally and a different image when turned obliquely. Actually, I have been unable to see the second image.

There is no engraver listed for this stamp on their site and I am wondering whether it was engraved by hand or was this an early form of "computer assisted" production. Looked at closely, they do not appear to be machine engraved but if done by hand, the engraver would have had to learn a whole new technique and deserves recognition.

Here you are - the official Canada Post word from March 1974