It is excellent that you are working on a platinum coin ring! This metal can be a bit tricky. I generally recommend trying a gold coin first but it sounds like you have the skill sets to do platinum. The first one is always the most exciting!
Here are some points of interest I have learned about platinum:
1. It anneals similar to silver and gold. Take to a dull red heat in a pitch black room, let cool to a dark heat and quench in cool water.
2. Ferrous metal can stain the platinum, especially if the platinum is hot. I use copper tongs/tweezers to grab the coin when I am annealing.
3. Because of the stain issue, I use a separate set of brand new finishing tools for platinum like the buffing blocks, tweezers, burnishers, etc. I use the standard Jason’s Works (JW) forming tools and techniques when shaping.
4. Platinum can get an “orange peel” surface if stretched or reduced a lot. I limit the size options for rings due to this. Platinum is very very dense so a 1 ozt coin is about the size of a silver half dollar. Size 9-12 would be ideal for an American Platinum Eagle. I try not to overstretch as much as I usually would before reducing because of the orange peel issue. I’ll use a JW stainless steel and plastic folding mandrel or cone to stretch the cut side to shape. It is a very interesting feeling to have such a small ring weigh so much on the finger!
5. If using an American Eagle, I like a wider band to keep the date as much as possible.
6. Platinum does not polish like other metals. It has more of a smearing characteristic. The metal is not really removed by filing, sanding or buffing. It is kinda sticky, per say? That is one reason people like platinum rings as they do not wear down as much over time by the loss of metal. In order to get a high polish on the cut side of the ring you will need to use a burnishing tool. This will achieve a high polish for you. I use the white side of the Sally’s Miracle Buffing Block to polish the rest of the ring. It is more of a burnishing block on that side.
Hope this helps, I’m excited for you! These are fun to make and a great skill set to have. Always nice to expand one’s knowledge and get the heart pumping when silver gets a bit mundane 🙂