Natural or manmade?

EDIT: Not sure why I'm getting downvoted, I'm asking for clarification. Are people not aware natural glass is a thing? Obsidian is a glass, for example, and has historically been used.

The earliest glass dates back to the middle bronze age in Egypt and Mesopotamia. Egypt is often assumed as the origin point because of the production of faience, a sort of glass like material most famous today for its use in creating scarabs. Partially supporting this is that very early glass does tend to be Egyptian, but on the other hand there its considerable more work done in Egypt of that period than in Mesopotamia. These earliest items were beads, although by the late bronze age it was used for more things.

Glassblowing was an innovation of the classical and particularly Roman period, and allowed for a huge increase in the amount and quality of glass used.

The earliest glass was crushed and cold worked in molds. As /u/Tiako says, it was probably in Egypt and Mesopotamia, and it was used in Inlays and small beads and the like. The composition of the glass was different than how it is today, and so the glass was not clear as we think of glass today. It was probably meant to imitate jewels. For more on the subject see:

Wright, Karol "Molten Color: Glass Making in Antiquity" 2011

Shaw, Ian and Paul T Nicholson, eds. "Ancient Egyptian Materials and Technology" 2000