I punch rock and wood slowly everyday; is it good for conditioning knuckles? What do you recommend for conditioning knuckles? I am doing knuckle push ups on concrete, too.
In case you haven't seen it, here is a related question.
While you can punch rock and wood to condition your knuckles, you should do it with moderation. There is no quick way to condition your knuckles - it must be done progressively over time. It is really important to avoid injury not just of your knuckles but your carpals (wrist), metacarpals (hand) and phalanges (fingers).
Typically with conditioning exercises the idea is to slightly injure the affected area before allowing it to heal, then repeating the process hundreds or thousands of times. That healing process is very important - you might get better results if you only condition your knuckles once or twice a week rather than every day (eventually knuckle press ups on concrete will cease to have any measurable effect on your knuckles so you should be able to still do those every day).
Of course measuring progress is going to be difficult. You could use board breaking as a measure, or discomfort (or lack of it) when doing knuckle press ups on hard surfaces. In any case there is no standard or established way to measure it. Deformity or callusing of the knuckles should not be used as a measure or indication (ideally you want to harden the bones, deformity can indicate breaks and calluses are simply a toughening of the dermis layers).
I second coinbird's motion: don't do this.
There is a theory called Wolff's Law, which is a medical concept first studied by a German surgeon Julius Wolff back in the 1800's, and he found that microfractures of a bone develop under extreme conditioning, and the body responds by shoring up the fractures with calcium. The body, ever efficient as it is, finds that the most reliable source of calcium is from the bone itself - usually, from an uninjured area, and, coincidentally, behind the fracture.
His observations are correct, but further study of this phenomenon has created several counter theories, and so this subject is debated. One of the counter arguments to inducing Wolff's Law is that when robbing the bone of calcium, that part of the bone becomes extremely brittle. So in a normal bone, you have a mature and evenly distributed amount of calcium. In inducing Wolff's, the front of the bone is very hard, but the area behind it is brittle, and is subject to forces other than that which triggered Wolff's to begin with.
A corollary to Wolff's Law is Davis' Law. Davis is similar, but doesn't apply to bones: Davis applies to soft tissue. Davis' Law was discovered by another surgeon, an American named Henry Davis - also back in the 1800's. He found that soft tissue heals according to the stress it is placed under, in order to protect itself from that stress. In short: calluses are developed in response to that stress. The issue here is that calluses can develop painful spots in areas other than the callus itself. That can affect nerves, which can be hyper-sensitive to the pain; it can also cut off the nerve to the nervous system, causing the opposite - no pain at all.
In both phenomenon, osseous and soft tissue will revert to normal once the stress heals. In Wolff's case, healing bone will not be uniform, and can create uneven surface on the bone, which can cause pain in the skin and tendons that run along it. And in the case of Davis, scarring can result. In other words, healing is imperfect - and sometimes that imperfection is permanent.
My suggestion to you and anyone who wants to do bone conditioning: use a punching bag.
If you have money, you can buy the full text of some of these articles:
Curious legal issue surrounding Davis' law:
Here's some more advice on advisability of such training:
Wanna see what happens to this kind of extreme training?
No, that's absolutely not good for you. Your hands take enough damage in sparring and fighting. DO NOT PUNCH WOOD AND ROCKS!
Hit the bag with gloves (and wraps if it's a power hitting day). Hit the mitts. Your knuckles will be fine.
Professional fighter here. I've never heard of anyone worry about knuckle conditioning.