Richard,
The small battle at Lewisburg, Va on May 23, 1862 began when the confederate general attacked the 3rd Provisional Brigade of General Jacob Cox's Division, with 2,500 men. Colonel Crook commanded the union forces having 1,200 infantry, 400 cavalry and about 100 artillerymen with four to six artillery pieces. Gen Heth was defeated and fell back after a lively affair of a couple of hours. Four artillery pieces of the confederates were captured by the 44th Ohio Infantry commanded by Colonel Gilbert who described them as two 12 pdr field howitzers, and two 6 pdr rifled cannon. During the civil war, the nomenclature used to describe the cannon was a odd assortment of names often meaning the same gun. This is the problem you are having in determing what cannon you have. An example is that there was no 10 pounder rifles except as a misapplied name. Also, during and after the civil war, artillery pieces were much moved around, often changed in their assignments or destroyed. Little know is that many of the older types of cannon were smelted down and the metal was used to forge new cannon. I can not venture a quess what kind you are asking about. The real key information is forged on the cannon which identiifies the piece with question. If you provide that info then maybe the mystery will be over.
Ron

As Colonel describes the captured cannon as 12 pdr field howitzer or 6 pdr rifled cannon, both would have been made of bronze and not iron. Bronze cannon would have a green patina over the bronze finish and the iron would be a painted black color over the iron gun metal.