Hello,My name isCustomerand I would love to help. There were no photos of the piece that came with your original inquiry.Please use the Add Files feature on your screen to add pictures of the mark on the bottom and of the piece.
I will answer without pictures.
The Imperial Glass Co. made the purple slag glass round covered dish with squirrel finial (mold #821) between 1959-1960. It is unmarked and is about 5.5" wide. The book titled Slag & Marble Glass, The Prominent Years, 1959-1985 written by N. Taves & D. Jennings shows it on page 14.
The value of this piece is $120 to $140 retail.Some sites that I recommend for selling are Varagesale.com, Ioffer.com, OfferUp.com, Ebay and letgo.com.You can also go to invaluable.com or liveauctioneers.com and search their directory for an auction house near you and consign to them.
To finish, I will need you to click the five stars at the top right of your screen and hit the green submit button, thanks!