Blanks are made from carbon cloth impregnated with resin. This cloth is wrapped around a steel mandrel and taped tightly in place with a clear tape. This assembly is then put in an oven where the heat softens the resin allowing it to flow between the cloth's matrix. Removed from the oven the assembly cools and the tape is removed. It is the resin flowing between the carbon cloth and the tape which produces a spiral ridge on the freshly made blank. This is known as an unground blank, because all blanks which have a smooth finish have this ridge sanded away. These are smooth ground blanks.
|Unground (top) and Ultra Matt (bottom).|
Grinding a blank smooth mostly removes resin, but some of the carbon is also taken away. I have found, to my personal cost, that blanks which have been designed to be built up in the unground state can be softened a little if they are smooth ground. This only becomes noticeable in test curves of 2.25 and lower in my experience.
I assume this is because the same depth of material is removed to get the blank smooth no matter how thick the blank wall is. So on a thinner walled blank the percentage removed will be greater than on a blank that has thicker walls. I therefore recommend taking care if wanting a smooth blank from any of the lighter models of Harrison's earlier blanks.