De or het stamping?

The correct Dutch article is:

de stamping

Rule Words ending in -ing: almost always de. See the rule

How to use stamping

the stampingde stamping
this stampingdeze stamping
that stampingdie stamping
our stampingonze stamping
your stampingjouw stamping
every stampingelke stamping
which stamping?welke stamping?
a big stamping / the big stampingeen grote stamping, de grote stamping

Dutch words ending in stamping

aanstamping

In compound words, the last part decides the article. See the rule