Question for a lawyer
 

I'm writing a story about a patent dispute that took place in about 1940. I have written the sentence below, but I am not sure about the phrase, "part of the public domain." I'm not sure "public domain" is the right term. Can anyone advise me?

"Patent law at that time held that once a product is on sale for two years its design becomes part of the public domain and cannot be patented."

I think that is a correct usage. You tend to hear the term "public domain" more in connection with copyright, but it is technically appropriate in the patent context as well. The alternative term you'd hear in the patent context is "not patentable".

When I applied for the patent I currently hold, the two issues the attorneys raised were 'prior art' and 'how long have you been selling this unpatented?'.