I did a bit of searching over the weekend to find other examples of these knives to see if I could piece together a chronology of when they were made. I'll preface this by saying please don't flame me off the forum for being dumb and simplistic without reading my many caveats! Here is the hopelessly oversimplified equation I came up with to determine the age of a Iwasaki Tamahagane Western Razor:
Date of Manufacture= 1946 +(Lot# * 4.5/213)
Here is how I got there:
I learned from Takeshi's email (posted in this thread) that Iwasaki generally made the razors (not knives ww243) :) in batches of less than 10. This matches my own small research sample; I haven't seen any examples over 9, and the average (median) inspection number is 4 (see the table below).
Additionally, I learned from Takeshi that half of the razors that were made did not pass inspection (same email).
Additionally, I've read in many places that Iwasaki stopped making the Tamahagane Western Razors in the 1980's. The best account is from Jim Rion of Easternsmooth who went to Sanjou to interview Shigeyoshi Iwasaki 4 years ago.
Iwasaki-sensei: Lessons Learned Part 2 | Eastern Smooth: The Blog
And lastly, it's widely known that Kousuke Iwasaki founded the Sanjo Workshop in 1946 (From the preface to Jim Rion's Translation of "Honing Razors and Nihonkamisori". Thanks again to Entropy for attaching a copy of this book in an earlier post.
So to make an (admittedly terrible) estimate of when a particular Iwasaki Tamahagane Western Razor was made, I used the following assumptions below to arrive at the following.
Assumptions:
1. Average lot size for Iwasaki Tamahagane Western Razors (ITWR) is 9 razors
2. Average Yield 4.5
3. Year that Iwasaki Tamahagane Western Razors first (ITWR) made is 1946
4. Year that Iwasaki ceased producing ITWR for sale is 1985 (all I know is "mid 1980's" I assume 1985)
5. Years of Iwasaki procuction is 40
6. Oldest know razor lot # is 1901 (from observed examples in table below)
7. Total Razors produced is 17109 (from assumption 1 above * assumption 6 above)
8. Total ITWR razors produced meeting quality control standards and sold 8555 (assumption 2 * assumption 6)
9. Number of razors produced and sold per year is constant (terrible, hopelessly simplistic assumption for estimate purposes)
10. Number of razors produced per year for sale/use is 214 (assumption 8/assumption 5)
11. First razor produced was 1.1(I realized I was assuming this just before posting, didn't want to renumber 'em all)
So for a terribly rough estimate based on the assumptions above, you can estimate the age of a Iwasaki Tamahagane Razor by dividing the lot number by 47.5 and adding that result to 1946.
Date of Manufacture= 1946 +(Lot# * 4.5/213)
This is obviously a very poor way of estimating the age of a razor, but it's the first time I've ever seen anyone even attempt to do it, so it's meant to be a start, not a good solution.
The weakest assumption is of course that the number of razors produced per year is constant. For all I know, they produced 99% of them in the 1960's when Kousuke Iwasaki was wrote his lecture at the barber college. The best way to get a good estimate would of course be to get a photo-copy of the inspection log book from Sanjou Seisakushou workshop (not gonna happen).
If this looks quixotic to you, it is. I'm now really fascinated by this razor and I can't help myself. I'm guessing some of these assumptions are off or dead wrong, and I'm hoping that folks will chime in to help improve them. It's a rough start at best.
Here are the Iwasaki Tamahagane Razors I've been able to find on the internet with legible Lot and inspection numbers.
http://i1271.photobucket.com/albums/...psi7atabka.jpg