Can honestly say I've been doing more bottle digging and metal detecting the last few years than insulators. Occasionally an insulator will pop up in one of my dump spots, usually nothing special. This particular dig in an old hotel/boarding house pit produced a lot of medical bottles, blob tops and flasks.

This light cobalt U.S.A HOSP. DEPT. bottle is attributed to glass factories in Baltimore circa 1863 to 1865. They were also made in Pittsburgh though the bases are different. I believe this was the smallest size. They were issued in surgical kits for the union army and their use continued into the 1870s though mostly in the mid west. This particular embossing variant is one known to have been used during the Civil War period. Clear and aqua are most common, rare colors are Green, shades of cobalt and puce ( think that great brown amber all colors mixed together Brookfield B beehives)