I have not yet found much about a sewing machine with the trademark of "Black Diamond". I did find 2 online sale posts for what the sellers called a Black Diamond sewing machine.
One was on LetGo.com with an asking price of $3,000!!!https://us.letgo.com/en/i/black-diamond-sewing-machine_e03feabb-49a7-4801-8fc0-adf68afa7adf
But . . . the name on the sewing machine (image is upside down) looks like *orleigh Diamond".
The other was listed on JLA Forums, with the asking price of $30 (posted 24 Feb 2012.)http://www.jlaforums.com/viewtopic.php?t=129527357
Could "Black Diamond" be part of the model name and the maker of the sewing machine from one of the major sewing machine manufacturers, such as Singer, White, Husqvarna, or something else?
Is yours a vintage or antique sewing machine?
If you can take a photo of your machine and save it as a JPEG image on your computer, you could then post it as an attachment to your question. Seeing an image may enable me or someone else to identify the make of sewing machine and then provide you with sources which may give a sale value.