Gentle Galoots,

Ken Shepard wrote, very helpfully:

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Philip asks about how to determine the "grit" of a stone. I don't know
about other materials, but the various grades of Arkansas stones are
determined by specific gravity. The density standards for Arkansas
stones are as follows:

Soft Arkansas 2.20-2.30 Hard Arkansas 2.30-2.45 True Hard Arkansas 2.50+
Black Arkansas 2.50+

So now you want to know how to measure the specific gravity of a stone?
Specific gravity is the ratio of the density of the object to the
density of water.
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I was inspired to grade my Arkansas stones by determining their specific
gravity. I used a different method. Since the density of water is 1.00
grams per cubic centimeter, then the specific gravity of an oilstone is
simply its density in the same units (g/cm^3) divided by 1. I used a
digital kitchen scale that can be set to measure in grams. (All of this
is at 4 degrees C, which is about the temperature of my shop.) Here is
what I found for 5 stones:

Stone 1: Black Arkansas, 2.67 g/cm^3 Stone 2: Translucent Arkansas, 2.87
g/cm^3 Stone 3: Unknown Arkansas, 2.24 g/cm^3 Stone 4: Unknown Arkansas,
2.17 g/cm^3 Stone 5: Unknown Arkansas, 2.28 g/cm^3

If you had asked me before I took my measurements, I would have told you
that stones 3 & 4 were soft Arkansas and that stone 5 was hard Arkansas.
Now I would say that stone 4 is probably a Washita, stone 3 is a soft
Arkansas, and stone 5 is an "almost hard" Arkansas.

By the way, someone wrote earlier (sorry, I lost track of who it was)
that you can judge hardness by the scratch pattern. I have noticed on
the 3 softer stones that if I press really hard, I get noticeable
scratches and relatively fast action, but if I press down less hard and
move faster, I get a much shinier result.

This has been an interesting exercise. Thanks, Ken, for the information!

Chuck Taylor north of Seattle


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