The facts are:
A.) The Tilson coat is sewn with logwood dyed linen thread (some of it has oxidized to brown/tan, some is still dark blue-black) and has gimped black silk bar buttonholes.
B.) The Henderson coat is sewn with a very dark blue indigo-dyed cotton thread and has gimped black silk keyhole buttonholes.
Getting logwood dyed cotton or linen thread that is the correct color is near impossible. Getting real indigo-dyed cotton thread is just as hard. Your first option would be to purchase Coates & Clark Button and Craft thread in black or chona brown. While it's a cotton-wrapped polyester thread, it's size and appearance is very close to original thread. It is also going to be stronger than thinner, all-cotton thread.
Your second option would be to find size 20 or 30 cotton crochet yarn (the type in the ball, not the embroidery floss stuff). This is hard to get in the right color so if you have time and want to make a mess, you can try dyeing it with RIT dye.
Finally, some tips on buttonholes. Silk buttonhole thread is available at the link below. You can make either the "keyhole" style of buttonhole or the "bar" style. Measure the buttonholes twice and cut once using a 1" or 1 1/4" chisel. The bottom buttonhole on Sharpshooter frocks is always on the body/skirt seam (a common feature of Schuylkill Arsenal frocks, who made the U.S.S.S. uniforms). I could go on for a while but you can find tutorials online after a quick search.
http://www.bblackandsons.com/sewing-sup ... 1fecd7d36chttp://static.colettepatterns.com/conte ... 00x750.jpgI too will be making my own U.S.S.S. frock this year...can't wait to see how yours comes out! If you have any further questions feel free to drop me an email at
brian@wwandcompany.com
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Brian WhiteWambaugh, White, & Companyhttp://www.wwandcompany.com----------------------------------
Randolph Mess, U.S. Sharpshooters