Blakksmyth

You can reduce bending of the stock by doing a couple of things. Firstly rotate the stock 90 degrees after every blow, if hand upsetting, and secondly hammer a small chamfer on the edge. For instance, if you are upsetting 3/4" square stock put a 1/4" chamfer around the edge before upsetting. It doesn't stop the bending completely, but it reduces it a lot.
Good Luck.

Cheers,
Rob K

I use equal parts of bees wax, linseed oil, turpentine and Japan black(Dryer) for inside work. This can be applied to black heat ironwork. The mixture sets hard when cold, but can easily be melted before use, and it smells nice to boot.
On outside work where you want the natural forged look I use a product called 'Penetrol'. It is a mixture of oils with a hardener added. It must be painted on cold and can be applied to milled steel, forged steel and even rusty steel work, and will maintain the look of the original finish. I guess you could say it is a cross between wd40 and polyurethane.