+1, I've got some that are 100 years old .... no, I didn't buy them when they were new. :D
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I doubt accuracy down to 1 part of oil is important. If it is, use the pharmaceutical aliquot method. Whatever measuring devices you have in your kitchen will probably suffice, and very accurate measurements are possible.
http://pharmlabs.unc.edu/labs/triturations/aliquot.htm
I'm doing the same thing for my son. In the process I found a German razor marked with the Star of David. I had Lynn hone it and I gave it to my Jewish dentist. He came to tears as he looked at this beauty, almost 100 years old with ivory scales. There are so many choices for you. Take your time, get one that YOU like and use. Your grands will cherish it and bless you for thinking of them. (You might need more than one razor.) Have fun.:boohoo: