A liquid metal ion source operating with an Er-stainless steel alloy was developed and investigated for focused ion beam applications of erbium as well as of several metal ions which are of interest for optical and semiconductor investigations. This alloy consists of a mixture of Er₇₀Fe₂₂Cr₅Ni₃ and has a melting point of about 860°C. The wetted-needle-type tungsten emitter showed a stable emission behaviour down to 1 µA emission current. The I-V characteristics, the temperature dependence of the extraction voltage, the mass spectrum and the energy spread of the main beam components depending on the emission current were investigated. While in the case of singly charged metal ions the beam is not defined due to isotope interference, in the case of doubly charged ions the species that are well separated for focused ion beam applications are available.