The fibula was used as a clasp to fasten the edges of the cloak together and keep it snug around the body. They are of several types, but the ones displayed here are of two differen varieties, both made of bronze. One variety of fibula the author has seen consists of a ring about one to one and one half inches in diameter, a looped piece of metal. and a pin Another variety looks and works much like a large, ornate safety pin. One of the things that has always interested the author is the area of Roman metal working and metallurgy.
The making of springs is a rather complex technology, involving not only close control of the alloy and composition of the metal but also the degree of work hardening or heat treating the finished metal object receives. First, the bronze would have to have a rather high tin content in order to impart the proper hardness to the alloy. Then, to form the spring into a coil, the piece would have to be annealed, or heated up and cooled down slowly in order to make the bronze soft and easy to work. Then, a second heat treatment process involving heating again and cooling at a controlled rate imparted springiness to the fibula.
These two fibulae have a catch on the bow shaped clasp part and a small bronze coil spring providing tension to hold the pin closed against the catch. After 1600 to 1800 years, the springs have retained their springiness and the fibulae, though covered with gray - green oxidation, function as well as the day they were made.