You guys have way too much time on your hands!
x2..
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I just finished a 170 gm jar of MdC, and I got 180 shaves out of it, being neither very stingy or wasteful. This is consistent with results that others have had.
It sounds like you will finish this report sometime in 2014. Your findings are bordering on pushing the number of uses over 1,000 which is so far from the results of the average use being reported by others, I think there is something else at play. All of my favorite soaps (generally Italian soft soaps) cost under $10 and I enjoy both their performance and not worrying about how many shaves I can get from each tub.
I primarily use creams, out of a $2.20 (full retail price at my grocery store, occasionally discounted) tube of Palmolive lather cream, I get roughly around 3 months of shaving. That is enough lather in a bowl to re-apply 3 times and still have a bit left over at the end. very effective on the hip pocket and good cream too, just has a love it or hate it scent.
It probably helps that the Palmolive cream is quite firm, exponentially more firm than the Proraso cream, probably feels closer to the Proraso soap than anything else.
You get 4 passes out of that much lather? I think we've figured out the issue - you like an extremely thin lather.
What you have on the brush in picture #4 ..... that's what I use PER pass!
So...... we're a little bored at home, are we?
I think an easier, although slightly more time consuming, test would be to take a precisely measured sample and see how long it takes to shave through it.
WOW! Talk about over-thinking a simple, traditional practice.
FWIW, I used a single puck of AOS Lavender soap for a two-pass shave every day until it was used up. I did not skimp on the soap. I just lathered the way I always do. That puck lasted exactly 9 months. A puck of AOS soap weighs 95 grams, according to the label. Nine months is 270 days, not taking into consideration that some months may contain 31 days. Ninety-five divided by 270 equals 0.3518518 grams per shave. AOS soap cost is $26.00 US. That makes it 9.6 cents per shave.