Hello,
I have a plain platinum wedding band that I need to stretch, because my ring-finger is bigger than it was 10 years ago.
I have not tried doing this resizing procedure before.

Prior to stretching the ring, I wanted to anneal the metal to improve its ductility.
Here is what I did:
1) I cleaned the ring in a warm pickling solution of acetic acid (distilled vinegar) and salt (rather than using 10% nitric acid, for environmental reasons)
2) Then I heated the ring to a dull-red colour with a butane powered micro blow torch, then I let it cool naturally. (no quenching)

I then tried using a Rathburn ring stretcher, which I expected would be able to stretch the ring, but it seems to have no effect.
I measured the internal diameter before and after with a digital vernier and it was unchanged.

The ring's inner diameter is 17.5mm
The ring's band has a comfort-fit cross-section, 2.4mm thick and 4mm wide.
It weighs 10g

So, what if anything am I doing wrong, or do I just need a bigger hammer for such a strong ring?
Thanks