Achieving rusted/ iron oxidized effect on the sculpture

Hello good people of ceramic community. I created series of animal masks (that I photographed just in case before first firing) and now would love to take it further and created rusted effect on them as on the second photo. Does anyone has any experience in getting similar effect? I would prefer to do it in underglazing stage - but then again my glazing knowledge is very limited so any tips would be much apracieted - I'm planning to do some tests with the use of any advice I can find. Thanks in advance for your kind suggestions :)