When using hammers and chisels safety goggles should always be worn.
This is the most common kind of chisel - a flat chisel. It's made of high-quality steel, and the end is tempered and hardened because it has to be harder than any of the metals you're likely to want to cut with it. The head of the chisel needs to be softer so it won't chip when it's hit with a hammer.
This is a cross-cut chisel. It's called 'cross cut' because the sharpened edge is across the blade width. This chisel narrows down along the stock, so it's good for getting in grooves. It’s used for cleaning out or even making key-ways. The flying chips of metal should always be directed away from the user.
The gasket scraper is not a true chisel. It has a hardened, sharpened blade and it’s designed to remove a gasket without damaging the sealing face of the component. The scraper should be kept sharp to make it easy to remove all traces of the old gasket and sealing compound.