The Isaac A. Shepherd and Company foundry, located in Philadelphia, Pennsylvania, started in 1863. Their cookware is normally gate marked common in the pre-1900s. You can see the gate mark clearly on this skillet. Thet were one of the few companies of the time to put identifying marks on the cookware. They bear an IAS and Company marking and a numbered back or handle. Very little information exist about this company other than the stove products it produced - the skillets are extremely rare and difficult to find.   No spin.  No cracks.  Sits perfectly.  Feel free to make an offer.