In apparatus for picking up a test sample of molten metal or metal alloys and measuring the cooling curve of said sample, comprising a sample receptor and an optical conductor leading from the receptor to a transducer, the receptor is a small, open ended refractory tube having a cavity for receiving the molten sample arranged at the free extremity of a lance with the optical conductor contained within the lance and terminating at the cavity in said receptor and a barrier is disposed between the cavity and the optical conductor, the barrier consisting of a heat resistant, highly thermally conductive material of such quality as to cause the material of the melt sample which is picked up to adhere thereto.