The Byzantine emperor, a Christian monarch who lived in Constantinople, needed help. He turned to the pope, who in 1095 called for all Christians to start a holy war against the Suljuk Turks. Thousands rushed to join the Crusader armies. They crossed into Palentine and recaptured the important cities of Nicaea and Antioch. Jerusalem fell in 1099 after a desperate siege lasting six...

Traditionally, glue is made from boiling up the bones, skins and other parts of animals such as fish or horses in order to extract the gelatin, which is then purified and concentrated to make a sticky substance that will form a bond as it dries. There are now many different types of glues, made from plant material or minerals such as petrol, as well as different kinds of synthetic...

There are a few factors that govern how valuable a stamp is to stamp collectors: the most important is how rare it is. Obviously, very old stamps are uncommon so these, such as the ‘Penney Black’ very seldom come up for sale and so are unbelievably expensive. Other things that might make a stamp rare might be where a mistake was made in the printing and the stamp was withdrawn after...