Platinum Ring stretching problem

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

Dear Nicholas,

Those ring stretchers are barbaric and unpredictable. When it does work, it will be in leaps and bounds. I wouldn't give it house room.

What you need is an upright ring stretcher, where you use gentle leverage and watch the ring descend, measuring intermittently with a separate ring stick, or in your case your finger.

A jeweller can do it for you, or you can join a class. Dennis

Dear Dennis,
Your reply only obliquely answers my question.
Am I to infer that I wasn't doing anything technically wrong in the process, and that merely a greater and more evenly applied force is required?

Regards,
Nicholas Lee

My reticence has a purpose. I have often enlarged gold and silver rings buy stretching, but platinum is not in my field.

As far as I have read it is capable of being annealed by heating to an orange colour and then quenching, but I would hate to have you damage your ring. Hence my rant about that primitive ring stretcher.

I also understand that platinum is easily contaminated when heated, so it should be done on a fresh clean surface.

Other members here have first hand experience of platinum, but I'm afraid they will be involved in the usual end of year rush. Dennis.