I've been shaving with DE razors & blades -- plus occasional straights for several years now -- and thought I had the technique down pretty well. Rarely do I get any nicks or weepers. And I can face lather cream or soap, use both hands, and shave every day with rarely any irritation.
However recently I noticed an unpleasant burning after shaving and wondered what happened to my technique. Wasn't using a dull blade and wasn't bearing down more than usual. Nonetheless I lightened my touch, changed my Iridiums more frequently and shaved every other day.
Then I decided to do some more controlled tests -- using the same razor -- a Rocket HD, but swapped blades, brushes, and soap or cream. It was a bit frustrating that even with a new blade and a great lather, finishing with alum & witch hazel, I still found my face reddened and burning -- even 8 hours after shaving.
But then an insight -- the quality of the soap or cream might be the culprit. I thought that these products had an almost indefinite shelf life, but Tabula Rasa -- that great handmade soap/cream from Lees -- was one problem. I hadn't used it in a while, but it smelled fine and lathered great. But produced a real irritation. Annoying since almost half is left after 1.5 years. Then I discovered that once I had began using my Cella cream again -- it too was leaving a real razor burn sensation. It was a little over 1 year old. Ditto with Proraso cream. But maybe it is only creams that have limited shelf life.
When I switched to GFT Rose or Almond soap -- no problem at all. And in fact since I was being super focused on my technique, lather & etc., the shave was smoother, closer, and irritation free. Just another discovery on the path toward shaving nirvana.
And I thought others might be interested in my discovery.