617. Fuels Prohibited for Shabbos Lamps
The fuel for the Shabbos lamp must draw after the wick. Fuel that does not draw after the wick may not be used. Examples include tar, beeswax, oil from a gourd, fat from a sheep tail and tallow. We may not light Shabbos lights using wicks that do not catch well and fuels that do not draw after the wick as a preventive measure against the possibility that one may come to tilt a dim lamp in order to improve its light.
One may light with tallow or with boiled fish innards if they have been mixed with a little oil. Other prohibited fuels may not be used even if they are mixed with permitted fuels because they still don’t draw.