... And ...
What is the maximum duration to hold these hot objects and what is the cool down time (the time from releasing one object to picking up the next).
How long can they be from the fixture point.
Materials like cast iron and stainless steel transfers heat relatively slow, but keep the heat for quite a while. Aluminum OTOH picks up the heat very fast, but dissipates it fast as well - with careful selection of materials and design/construction, it could hold metal glowing cherry red (for a certain amount of time).