What was the name of the famous interior designer? Perhaps the interior designer specialized in recommending or supplying certain types of art to people that might be possible to be found in searches on the Internet or in books.
What I would suggest doing is taking the work of art to a college art professor, art gallery, or even an auctioneer for the identifying the artist. You also might find some monotypes listed in books at a public library with maybe even auction or sales prices listed. On the following searches, you might find items to be similar to the one that you have, and that might give you an idea as to how much monetary value something like this may have.
monotype eBay - Google Search monoprint eBay - Google Search