Trying to do at least one post a day.
In my opinion, your two buttons are not made of brass, nor are they silverplated. Note that they are flat with the loop embedded in a solid metal cone.They are made of a metal which Metallurgists call "White Tombac", to distinguish it from simple Tombac, which has a "dull golden" (not yellow or bronze) color. Excavated White Tombac has a dull-silvery color. It is a brass-alloy, containing about 85% copper, 14% zinc, and 1% Arsenic. The presence of Arsenic changed the brass alloy's golden color to silver-ish. Apparently, that very small amount of Arsenic is enough to inhibit the bacterial action which puts a "patina" on the metal in the ground. White Tombac buttons typically come out of the ground with very little or even no patina on them. You'll notice that your smaller White Tombac button has a little dirt-crust on its face, but most of the dull-silvery color is showing even without you cleaning the button. The button-dating reference I use says "about" 1750 into the very-early 1800s.
Sidenote, about "regular" or "simple" Tombac:
During World War 2, Canada made its 5-cent coins out of simple Tombac. In photos of uncirculated ones, you can see the "dull golden" color. Check the photos below. One shows the Canadian 5-cent Tombac coin, and the other shows a White Tombac coin from Romania.
