ANACS - 07 Silver Eagle Toning In Holder?

Also if there was some type of contaminant present on the edge of the coin it can still react with the air and whatever water vapor may have been captured inside the slab when it was sealed. So yes coins can still tone inside of the slab. The early NGC slabs are known for this with silver coins reacting to outgassing from the label. If you ever have a chance to look at roosevelt dimes in the first five NGC slab generations you will see that almost all of them have a nice rainbow tone on them at the point where the coin is closest to the label and the tone is stronger on the obv than the reverse because that side is closer to the label. But from the NGC 6 slab on after they started the keyed insert (that groove in the center insert between the coin and label.) that toning almost completely disappears. (Probably many of the ones seen in the later holders are crackouts from the early ones.)

Hey I love toned coins graded or not!