Odd question but lets all take part in answering

[Paul B]

paul might not be the longest reefer on here,

Great, I don't want to be known as the oldest geezer on here.

My current reef tank (the tank itself)was my granndfathers bought in 1920 something I think he said.its been passed down...really cool tank tt gallon no center brace....still original silicon.

If it is from the 20s, it is sealed with tar. Silicone came out in the 60s.
Is it black stuff?