This is a small, tipless carbon filament bulb, with a deep Ruby Red envelope. It is quite heavy for its size, with a very thick glass envelope. This bulb may have been meant for use in a darkroom lamp, for developing black & white film. Tipped red darkroom bulbs are fairly common, but early tipless versions like this one are not. The filament in the picture of it lit appears to show a purplish/pink color, but in reality it gives off a deep red hue. Here's a picture with much more accurate color. Although one might be tempted to say that this is a vintage light bulb because it lacks a vacuum tip, I believe this bulb may be one of the earliest designs of tipless bulbs, back from a time when you had to specifically special-order them to be tipless. I believe this because the lead-in wires seem to be made of platinum (as far as I can see, the glass is so thick and deeply colored that it's real hard to see the inside, even against the sun), and because I do not see an exhaust port inside the stem. But since I am not entirely sure it is a genuine "early tipless" bulb (made in 1906-1910), it will remain in the vintage gallery, since it is well known that tipless bulbs went mainstream in 1922. Though just going by how thick the glass is, it might be antique.