Very easy and natural.
Here's what you need:
2 soft bristle tooth brushes
Cream of tartar (large container)
1. Dry brush the bullion and try to clean any dust, dirt or debris off the item before you try and clean it.
2. Get the tooth brush wet and then sprinkle the cream of tartar on the item to be cleaned. You want to gently scrub with the tooth brush until you create a paste with the cream of tartar and the water.
3. Keep adding equal amounts of water and the tartar and keep scrubbing in either a circular motion or with the grain of the bullion. Don't scrub too hard. remember the bullion thread is delicate. Go through it patiently and take your time.
4. Rinse the tartar off the bullion to evaluate your work. Repeat the process as needed.
5. When you get the desired luster or brilliance back, rinse the bullion to get as much of the tartar off. When you are done rinsing then blot to bullion with a paper towel until you soak up the excess water and let it air dry. Do not blow dry it, dry in the direct sun. In a day or two the insidnia will be dry and you will have brought back the original luster in your insignia.
Caveat! This will not work on all bullion insignia! Do your research, some bullion thread was electroplated silver on brass or copper, if the oxidation is too far gone, you may not want to use this method since the silver may have already oxidized off the insignia.
Try this method on a test piece first till you get the hang of the process then move your way up to a piece that you would like to clean.
A good way to determine if you are willing to try this method is to look at the bullion thread with a 10x jeweler's loop. you may be able to see if the thread has any copper or brass in it. If it does, it may not shine up as you may think.
Good luck and I hope this method works for you!
If you have any questions feel free to PM me.