I've heard that 14-carat gold is harder, but not as rich in color as 18 carats. What are the differences between the various gold types?

14-carat gold is hard but it is paler than 18 carat and also contains less gold, and is more likely to give allergy or corrosion problems depending on the wearer's skin. You will find some excellent articles at http://www.18carat.co.uk/information.html, which may help you make up your mind about which type of gold to have your jewelry made in.