Soldering artifact cause

Hi All,

This morning on the first job of the day (how often do you hear
that?) I was soldering the setting/finding to a 16K palladium white
gold ring with 14K ezy solder and when the solder flowed up through
the post hole (I was heating the setting) it took a considerable
amount of metal from the shank with it.

The ring was fire coated with boric acid in ethanol and borax flux
was used at the junction. The flame was slightly oxidising.

Now I feel that the inclusion of the shank metal into the joint will
lead to it being much stronger and a closer colour match all round,
but the pit is quite big and will need to be filled (I’ll use some of
the casting sprue solder into place). So what happened and why?

A couple of pictures are posted in my Flickr account
(solderpitflashpic | I soldered this ring this morning, the r… | Flickr) so you can see what happened.

Regards, Thomas.