It was the test on 2015 on the sample earpads, it is proved to be failed after a year when the glued earpads cracked opened after a month or two and claimed by the clients.
Now all the black earpads are glued by Aron Alpha wood and leather instant glue, expensive but effective.
The material of black rubber earpads is Nitrile Butadiene Rubber NBR, last batch was glue by factory, unaware that the negligent attitude of the worker almost destroy the whole batch, glue vapour made a white misty layer on the the rubber together with fingerprints, big glue drops, uneven contact…. All made my life very difficult and painstakingly remove and polish every pieces for every order.
Pre glue by factory is not an option, every piece has to be glue by myself. Ordered another unglued batch and needs a new glue for the task. The problem was not allowed to send glue by post, had to hand carry by friends with great thanks. Tests carried out on two brands; a. 3M no. 847 and b. Japan Konishi no. G103, both are claimed for NBR. Looks like both are fits for the task after 12 hours pressure applied. The 3m 847 failed after two weeks, just lucky enough before send out the headsets. The G103 is very strong, unable to separate the joints, still clamp it for 24 hour on every single pieces.