Damper springs on a square piano made by Tomkison estimated around 1790

Does anyone know in which material these black springs were made? Some suggested horn, horse hoof and whalebone. The material is definitely organic: when burning a tiny piece at the non-seen and non-functional part one gets a smell of burned hair/bone.

The form of the spring is roughly rectangular. The part that acts as a spring has been thinned from above.

Top view of the dampers and damper springs:

 

Detail of damper springs:

 

A damper spring removed (side view). The end part has been burned slightly in order to find out whether or not it's organic material.Note the taper towards the end. The material is quite stiff: