I can give you some generalities. I have read accounts of Confederate pow's carving items of bone /wood etc.early to mid 1863 .I don't know if the policy on having knives changed toward the end of the war.I suspect not as they were used to eat foremost.There are four or five species of the Cypress family including Southern Red Cedar that are found in the area of Ft.Pulaski. Cedar burns hot and fast.It is not good to cook with as it is very sooty and pops sending embers flying when in an open fire.There are many species of hardwoods locally that would make a better fire but, pending the Federal policies of the day that might be what they were given or could of foraged.Since the POW's were returned to Ft.Delaware possibly Hugh might comment on their policy on knives.Good luck!