That's an interesting site.
I've always used the artists acrylic applied with a toothpick to the fabric side of the curtain. Same stuff for patching pinholes in a bellows.
In regard to quantity. It's a SMALL dab about as large as a period on your computer screen.
Marc thanks for the web link lots of good tips there.
John Thanks too, I have some black artists acrylic so I will give that a try on one spot and if ok will do the rest otherwise I will get some fabric paint.
Apug to the rescue, the repair man wanted £160.00 to fit a pair of 'used'
curtains he would have probably used the paint and pocketed the lot.
Waayyyyy back in the day(1980's) when I got out of National Cameras school.
They learned us'n how ta make new shutter curtains. Let's be facin' it they're a light tight fabric with a couple of ribbons on it made to roll up on a cylinder.
I wonder if the 160 reflects his time to disassemble the donor camera.
Many times the charges are not for what he does, but for what he knows