Nixie tubes are filled with the gas neon and contain very small amounts of mercury. In very rare cases, tubes may contain a small proportion of other substances, which may be deposited in the numbers. The deposit can cause parts of individual numbers shine less. The effect is called "poisoning" or "poisoning".

deposits may occur in numbers that light up at this point with low light intensity. A strong light intensity prevents such deposits.

To avoid possible precipitation, the light-emitting brightness can be increased. Regular superimposing dates can also prevent precipitation.

To eliminate the precipitation of a number, this number must shine with increased intensity. Nixie clocks are usually equipped with functions preventing and eliminating possible poisoning: At night all digits light up with high intensity.