Good morning Emily,
Welcome and congratulations on creating your ring and for teaching yourself.
To answer your questions:
- White post-pickle residue.
Looking closely at your ring, The orange bit is not the fine silver, I think that you have a touch of fire stain, as well. I have had this problem at times when working with silver. To prevent it you need to make sure it is protected with borax or your choice of flux. There is plenty on here about preventing fire stain and is very useful. The toothpick in your dremel with tripoli should remove it, just take it slowly. It will also remove the fine silver left from the pickle. You can also remove it with sandpaper. My advice is to start with a higher grade, say 400 max and work through to a finer one, I usually end up with 1200 grit before polishing.
- Smooth, flat texture and excess solder
The swirls are, I think a result of using the 3m radials, as has been said they are aggressive. There are a few different ways of getting rid of these. Rather than using the 3m radials, you could go through the different grades of sand paper or different grades of silicone rubber wheels.
If you don’t want a mirror finish, the way you finish your jewellery depends on what you want to achieve and I would recommend you experiment on scraps of silver until you are happy with the result.
The excess solder can be removed using a file to remove most of it and then going through the different grades of sandpaper. You will learn how much to use through practice.
For the final polish, as has been said, don’t use the 3m radials. I would suggest you try Cotton, or Calico wheels. If you use Calico wheels you need to prepare them to remove any loose threads and continuously check to ensure there are no loose threads sticking out. These can be burnt off easily.
I hope this answers your questions. If you would like any more information, pm me and I’d be delighted to help you.
Good luck with your jewellery and keep learning and experimenting.