If you haven't guessed by now, these are all solid copper heatsinks. It appears the fins are skived out from the copper making each of these an all one-piece heatsink. With the exception of the bottom, aluminum was used to secure the fins together with bolts as you can see by the picture below. And as you can see the bottom is very smooth and polished like a good heatsink bottom should be for best heat transfer. At times I'll use a picture from one heatsink to demonstrate a point instead of using one from each because both heatsinks are identical, except for the width of the fins, as you see on the lower picture.

The 6000cu has 56 fins in that flower design and it's 2 1/4 inches across (I hate the metric system) and just under 4 1/4 inches long. The 3100-Plus has 54 fins and is 1 7/8 inches across and 4 2/8 inches long. The top part is cut even on the 3100-plus while the 6000cu has a coil-like look. Both have a groove cut in at about the center to allow the clip to be simply dropped down.