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Wet/dry paper around 220-400 grit, or higher, on anything flat (like plate glass or a marble/granite tile).
DMT D8C diamond plate used wet. It comes flat and works good. This can also work on your...

You might add something to your kit to flatten your hone.

I think Stamps222 on Eboy still sells Double Arrow razors for about $10 (less shipping). They make great practice razors and good shavers,...