Rod, your eyes might be telling your brain something different. He said pipe clay, not clay pipe. I'm assuming that it's a type of clay that could be used to make pipes once fired in a kiln.
jbird5986 ditto to what FishingRod said. Some other things to consider.
1) Don't make the sides steeper than 3:1 slope or you might have problems compacting the soil. 3:1 means for every 3' horizontal the slope drops 1'.
2) You HAVE TO compact the soil on the sides. You need to use a sheepsfoot roller, dig the pond deeper/bigger by 24" than what you want the finished size to be. A vibratory sheepsfoot is even better. You cannot properly "knit" the layers of soil together with a smooth barreled compactor. That pipe clay at the bottom?, bring it up and stockpile it at one place all by itself, don't mix it with other soil. Bring it back when the pond is dug, put a 6"-8" layer down and roll it with the sheepsfoot until the roller starts to "walk out" of the dirt and support itself on the pads, not the barrel. Put another 6"-8" layer down, repeat. Do that a minimum of 3 times, 4 times is better.
3) You CANNOT compact the pond sides/bottom properly if there is standing water in the pond. It has to be pumped out. I cannot stress this enough.
4) If the clay is too dry or too wet to roll into a pencil between your palms, it won't compact.
5) If you don't compact the whole pond, (up and above the high water line) it might not hold water as well as you want.
6) Any veins of sand or rock, dig it out at least 24" deeper than the rest of the pond and dig it out into the better layer of soil next to it. Compact that vein with the good pipe clay, again doing it in 6"-8" thick layers.
Look into talking to the guys at your counties NRCS office. They should be able to help you with the soil situation if they are any good. There are good and bad offices, I've run across them all. Download NRCS booklet "Agriculture Handbook 590". Spend some time reading it, twice if necessary before you spend any more $$. That will help you greatly.
Now if you end up needing a liner, talk to the folks at BTL Liners.
https://www.btlliners.com/ They can help you IF you do need a liner. Typically most liners need to be seamed on site, they can make up to a 30mm thick liner a hair over an acre in size in one piece. You will need some equipment to move it in place, and a bunch of people to unroll it, THEN equipment to cover the liner 12" thick with soil. Your equipment CANNOT come in contact with the liner or it has a HUGE probability of ripping it. If doing the liner, remember that you have to over dig the pond to compensate for the dirt that will be placed on top of the liner.
