red & black on 100 year old paddles

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I have several of these, each having survived the years in differing condition.

On some, the black is dried and cracked like clay in a dry mud puddle. It must have been applied in some medium like petroleum jelly or wax.

On one, when I slid off the case I could plainly see fine powder on the red side and get it on my finger.

Given the instructions = 1st red then black, my hypothesis is that the red is iron oxide and the black is plain carbon as soot or lamp black.

Any thoughts ?

Pretty sure you are correct on the red = iron oxide. No idea on the black, but sounds plausible to me.

Just a guess,
Red is usually a Rouge (red) oxide of iron) and available in many grit sizes. It differs only in grain size from polishing rouge..
Many dark razor strop dressings were made of a waxy substance and extra fine emery AS darker oxide of iron) which breaks down quickly. My favorite is "Radio" strop dressing.
Iron and other oxides all seem to be crystalline in nature and so do make abrasive compounds.
Lead Oxide was...and probably still is used in linen strop dressings. Hard to find anymore on a tube.
~Richard

An old barber I know has his dad's old paddle along with 2 crayon type dressing sticks. 1 red and one black. Quite hard waxy type crayon. May be boron in the black as well