The dragon can be a huge creature depending on the breed. The one shown here is roughly 20 feet long with a wingspan of 35 feet. This type of dragon has extremely small ears, large eyes, spines down its back, and a bone-type spade at the end of its tail. All dragon breeds are different. This type of dragon also does not have scales, it has tough leathery skin.
Most dragons have scales of some sort.
When born, a dragon's scales are as soft as tissue paper, and slowly harden while the dragon grows. The iron from the blood, or vegetable matter the dragon eats is absorbed by the dragon's blood stream and mixed with the keratin to create steel-hard scales. The process of getting scales as tough as they can get takes about one year after being hatched. Usually only red dragons will mate with other red dragons, etc. But if a mating took place between a gold and a green dragon, the result might be a bronze colored offspring.