What Are Blind Perfs

Do blind perfs affect the value of a stamp?

Unknown, I'd guess it depended on the stamp in question.
Blind perfs are indentations or similar, in the stamp paper, due to the puncturing pins failure to penetrate the paper successfully, due to wear or multiple sheets attempted.
Canada example

See SCF glossary over to the left under navigation for a definition start.

Blind perfs happen when the perforator pins do not go all the way through the paper. A small indentation will show where the perf is supposed to be. Happens quite a lot on coil stamps but I do not know how it affects the value


Peter

DrGG,
Generally speaking blind perfs do not adversely affect the value of a stamp. Have sold many stamps with blind perfs, and no change to value.
Generally speaking, they can often be removed very carefully by those who wish their stamp to have that "stamp shape", buy using tweezers and a very careful hand. BUT, it's not without risk in trying to remove them, so consider your skill, and the value of the stamp if you choose to do this.

In German philately, there is related, but slightly different phenomenon. On the old stamps, there is what is known as FZL "fehlende Zahnungslochungen", or missing perforation hole(s). These are caused by broken perforation pin(s).

THe expertizer has noted this on the stamp shown below.

Yes, missing perfs are another issue. And some blind perfs shouldn't be touched, because there is only the "impression" of a perf hole, but the pin did not actually penetrate the paper (or is less than 25% cut). Those you want to leave alone.
broken pens, or bent pens can leave missing or wildly out of alignment perfs.

Explanation as per SCF

Here is a Nova Scotia example.

I wonder if this terminology originated from the similarity of the raised, unpunched perforations on the stamps to the way the braille alphabet is printed?

Jim