Almost the Holy Grail

I have some pieces of black French cotton velvet that I use for 'total black' backgrounds that I bought in 1980, They are getting a little tatty and have always been frustrating as they are only 30inches wide.
The other day I bought a new black background that is enormous. About 9 foot by 12 foot. It cost just short of half a ton and promised a true black background unless one actually shone a light through it.
It arrived, I unpacked it, and, rubbish. I could virtually see through it. No way was it going to work.
Well, I thought I should test and here's the result. The left side of this picture has French cotton velvet, the right has some fancypants new see-through blackness.
And there's no difference. Well that was a surprise.