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I cut the leather off from one such strop, glued it to a board and abraded the top side with very fine wet'n'dry paper until it was velvety. It took CrOx powder very well and worked fine.
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The first one has just the flesh side of the leather at the back - a bit loose and open though. The other looks like a man-made material - try heating a pin head to red hot (hold it in pliers) and...