Do authoritative renderings exist for coats of arms? For a given surname it is easy to find many variations in its coats of arms*. I get the impression that coats of arms were described in records as text and thus were open to interpretation at the time they are rendered. Is this true, or are there actual interpretations of such descriptions that are more official than others? *I realize surnames may have differing coats (e.g., the same surname having different coats from Ireland v. England.) What I am interested to know is for a _specific_ coat of arms is one rendering the authoritative version versus another?

In England The College of Arms and in Scotland The Court of the Lord Lyon administer the granting of arms on behalf of the monarch. The right to bear arms is granted to individuals, not surnames or families (but it is inherited by heirs when the holder dies). The patent, a legal document that makes the grant of an Achievement of Arms, includes a description in words called a Blazon. The blazon is the legally enforceable description. Modern patents do include a pictorial representation which makes them very attractive, but early patents had no illustration. The blazon is written in heraldic language and describes how the shield is divided up, the colours used and the types and position of charges. There is some leeway for artistic interpretation. For example using a different shade of red (gules) or drawing an heraldic lion in a slightly differnt style would still match the blazon.

Fox-Davies A complete guide to Heraldry is a good reference for heraldic terms.