The double Stuivers in the coin hoard were lightly cleaned with a 15% Solution of citric Acid to expose detail hidden below the light layer of corrosion. Removal of this corrosion left a copper colour stain because of the high fraction (over 40%) of copper in composition of the coins.
The image of scans of the full coin hoard before and after the
cleaning have been displayed on top of each other for easy
Dutch 1670 Hoard Home page.