Polaris clock removal _ Polaris clock removal and installation

What is the handwriting on the old Polaris clock painted with?

Phosphorescent material. The words on the old Polaris clock are coated with phosphorescent material. A common phosphorescent material is radioactive tritium gas, which can emit weak green fluorescence. Tritium gas is a radioactive isotope with radioactive decay properties. It can release energy and excite phosphorescent substances to emit light.