Dural is a type of aluminum. Not very good for practice, The metal will stick to the tip of your graver. The best practice plate for the burin (push graver) is copper.
Also click on the link under my name below to go to my glossary (glosár). There you will find all of the tools designs and words of the engraving trade. Some are in German, Italian, and French. Sorry, no slovenský jazyk.
There is a pretty soft steel alloy called, I believe, ledLoy (or similar) that is just about as soft as you can get. I know it's available in round stock, I believe also bar, but I'm not sure about plate or sheet thickness. On the other end of the scale are two alloys, one of which I have, and will run cutting experiments on, named T-1 and Cor-Ten. Both, I believe, are USS patented products, and I doubt you could currently buy a small quantity. Both of the latter alloys were used to make the first space capsules, and are so hard that you almost don't need heat treatment. You just have to search the Internet, or go to someone who knows his stuff and has a decent scrapyard. Starting out, do not go to anything hard or tough. As you progress to tougher steels, you'll learn to change your tool geometries to suit the conditions. Good luck.
sybred: "mild steel" is a term we use for steel with a very low carbon content. any of the harder steels-- simply have more carbon added, as well as many other metals added to change the basic property of mild steels. one would think aluminum would be a good practice material. it's light in weight, but more difficult to cut than steel. if you do try aluminum, it's helpful to use a lubricant. kerosene and mineral oil are good to experiment with. take a small magnet to any scrap yard- most have many industrial punch outs, cutoffs, etc. all can be useful to practice on. these materials can be prepped using about an 800 grit final finish.