De or het soldering?

The correct Dutch article is:

de soldering

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

How to use soldering

the solderingde soldering
this solderingdeze soldering
that solderingdie soldering
our solderingonze soldering
your solderingjouw soldering
every solderingelke soldering
which soldering?welke soldering?
a big soldering / the big solderingeen grote soldering, de grote soldering