Alum is a no go for me, burns like hell! I’m in the minority of wet-shavers who doesn’t use ANY post-shave products whatsoever. No alum, WH, aftershave, nada. Just warm water to rinse the soap off and cool water to do whatever it does that works perfectly for me. I got to this method through trial and error and has been doing me very well a solid 8 months.
Dude...if the alum burns like hell, it probably means you are using your DE razor like a disposable cartridge razor. Not good.
And I use the word "Dude" in the most scholarly and collegial manner possible.