The first successful light bulb filaments were made of <answer>carbon</answer> (from <answer>carbon</answer>ized paper or bamboo). Early <answer>carbon</answer> filaments had a negative temperature coefficient of resistance — as they got hotter, their electrical resistance decreased. This made the lamp sensitive to fluctuations in the power supply, since a small increase of voltage would cause the filament to heat up, reducing its resistance and causing it to draw even more power and heat even further. In the "flashing" process, <answer>carbon</answer> filaments were heated by current passing through them while in an evacuated vessel containing hydro<answer>carbon</answer> vapor (usually gasoline). The <answer>carbon</answer> deposited on the filament by this treatment improved the uniformity and strength of filaments as well as their efficiency. A metallized or "graphitized" filament was first heated in a high-temperature oven before flashing and lamp assembly. This transformed the <answer>carbon</answer> into graphite which further strengthened and smoothed the filament. This also changed the filament to have a positive temperature coefficient, like a metallic conductor, and helped stabilize the lamp's power consumption, temperature and light output against minor variations in supply voltage.
What material were the first light bulb filaments made from?
carbon