Such was the success of Hill's uniform, weight-based postal system that within just 40 years of the first Penny Black, more than 150 countries had followed his lead and established similar systems. Excellence in design and production was a priority from the start and Hill even took the trouble to research an assortment of print methods which led to the development of a new `rotary' process. Security, to reduce the risk of forgery, has always been a prime concern, too, and Hill set a competition for the design of what he called `inimitable' stamps. For the first century of the British stamp's life most designs were simple and effective and have become known as Definitives. Today these everyday stamps are the simplest in design bearing the Monarch's head and the stamp's value or class of postage. The profile of the Monarch is a three-dimensional relief by the sculptor Arnold Machin. Scotland, Wales and Northern Ireland have their own version of the Definitive, for example, Scotland's includes an illustration of a lion rampant. The first stamps designed specifically to commemorate a major event appeared in 1924 to celebrate the British Empire Exhibition. This `special' issue was followed in subsequent decades by a handful of others to mark important events and anniversaries, but it wasn't until the 1960s that the regular issue of Specials was established. The Specials have more recently been joined by Greetings Stamps.