What are they?
Before all of the modern day self-adhesive stamps with die cuts, the sheets of stamps were perforated. All of the holes on the sides of the stamps were created by little metal pins that punched the holes.
Blind perforations are when the stamp appears to be missing the perforations, but if you look closely, there are traces of the perforation holes there.
How do blind perforations happen? There are several reasons.
First of all, one of the perforation pins may have broken off. Thus, the stamp has many perforations. But there is a spot where a perforation hole is missing.
Second, the perforation pins may become worn after extensive use. As the pins wear down, they don’t punch holes any more, they produce “dents” in the paper. The operator has to replace the pins with new ones that are sharp and will cue the holes.
Steel was in short supply in the US during World War II. If you check the Prexy series stamps (Scott #803-834) and other issues around this time frame, such as Scott #899, you can easily find stamps that are lacking one or more perforation holes. If the pin was broke or worn down, it didn’t matter if a few holes were missing or not. The stamps could still be easily separated even if some of the holes weren’t punched.
Here is an important point to remember. Blind perforations are not the same as missing perforations. This is very important for stamps that are imperforate or imperforate between. For a stamp to be truly imperforate, there can’t be even a faint dimple of a perforation hole. If there are any traces at all of the perforations, then it’s a case of blind perforations.
Sometimes I see pairs of Scott #899 that are described as “imperforate between”. In my experience, most of these pairs are blind perforations. Blind perforations are considered freaks and in many cases, they have some value to them, usually several dollars. But blind perforations are not as valuable as imperforates.
Once in a while I see a pair of Scott #899 and there is a single perforation hole between the stamps. Some people try to sell this as an imperforate between pair. It’s not. It at least has one hold. That makes it a less valuable freak.
When buying imperforate errors, check the stamps carefully. Are there any traces of perforations at all? By checking for blind perforations, you may just save yourself a couple of bucks by not buying the an incorrectly described item.