The bucket test is also a useful indicator.
You could even try two buckets and compare the sealing ability with poor compaction. Do one bucket as you describe above. Do the other bucket with no compaction (or moderate, dry compaction) and see how they compare.
One problem with the bucket test is that it does NOT measure the sealing against the entire water column. A 12' deep pond will put six times as much hydrostatic pressure against the clay seal compared to the seal in a bucket under only 2' of water.
That difference is significant. There are some people that have bottom leaks in their pond that lose water when the pond is full, but when it is down 5' the leak stops.
Also, IMO the bucket test overestimates the sealing capacity. I suspect 1" of good clay-bearing material would seal a bucket. That is partly due to the sides of the bucket preventing lateral movement during compaction. In a pond bottom, that is not the case.
Hope that helps. Good luck on getting your pond back into top form.
