when the jetons were produced many years ago the red inlay was plain. It happens to some old jetons that they look like a "bubble" after many years.
They inlay was produced with many layers. They used glue to put the layers together. After some years glue "vanish", and the layers starts to "bubble up".
I hope you understand what I would like to explain. It is not so easy for me in english.

Regards,
Bjoern Zabel
R-5585
www.casino-chips.de