Yes, ‘milk spots’ as someone mentioned, something to do with them not being rinsed properly before annealing I believe. Canadian 1oz silver maples are notorious for this. I have a tube of them around here somewhere that are very ‘milky’
The milk spots are from the acid bath, all plankets sp? go through. They are then rinsed in batches which cause them to not be properly cleaned.
I always clean my silver bullion in a quick 90% alcohol rinse. Don’t use 40% or it will leave the same mess.
Interesting info, thanks Saoirse and LOS3R.
--- Update ---
Yesterday evening I cleaned my silver round with boiling water and baking soda and I am very pleased with how it turned out.
It even took off the "milk spots"!
If interested in the steps I did, here they are, it only took about 15 minutes counting prep time.
Step 1.
Start boiling 2-3 cups water
Step 2.
Line a pan with aluminum foil & add in enough baking soda to cover a small area, about an inch bigger on all sides of what you will be cleaning.
Step 3.
Put your silver into the middle of your baking soda.
Step 4.
Add more baking soda, enough to cover your silver so it can't be seen.
Step 5.
Pour in the water after it comes to a boil. (If the baking soda on top of your silver washes off, you can put some more back on top of it.)
Step 6.
Wait 5 minutes. Then, using latex/rubber gloves, gently scrub the silver with the baking soda for 3-5 minutes. About every minute, dip back into the mixture of boiling water & baking soda to rinse it.
Step 7.
When you are satisfied with how it turned out, take off your gloves and wash silver under cold water for a couple minutes. (Taking gloves off help to not let more baking soda get on when you wash it, washing it takes off the baking soda so it doesn't leave a stain, & the cold water cools it off.
Tip: Use tongs to take your silver out of the mixture, as silver quickly gets very hot.