Under Irish law dating back to 1637, in the reign of Charles I, all Irish jewelry of precious metals must be assayed and stamped with the official hallmark - the traditional letter symbol for the year it was crafted, a fineness mark guaranteeing the purity of the gold, and the official insignia of the Irish Assay Office in Dublin Castle.

An assay is a test of the purity of an alloy. A tiny piece of metal is scraped from the piece and the percentage of gold, silver or platinum is determined. Official assay offices determine whether a piece qualifies for an appropriate hallmark. Gold jewelry is mixed with other metals and Karat (which means 1/24) denotes the purity of gold in the jewelry. 14k Gold is 14/24 gold mixed with 10/24 other metal.

The Assay Office is located in Dublin Castle. All Celtic cross jewelry and Irish Jewelry handmade in Ireland must receive a hallmark stamp from the office. A tour of Dublin Castle is a must for anyone interested in Irish history. The State Apartments stretch along the entire south side of the yard at first floor level. Portions of this section have been rebuilt numerous times. Though originally built to provide accommodation for the Lord Lieutenants (the viceregal representative in Ireland), they generally avoided living here from the late 18th century, choosing instead to reside in the Viceregal Lodge in Phoenix Park. They did, however, stay in the Apartments during "Castle Season", the period of official entertaining that started the first week of February and ended with a great ball on St. Patrick's night. Today the Apartments are used for the most important State receptions, also for the inauguration of the Presidents of Ireland.

Drawing on a rich tradition of celtic cross jewelry production which dates back to the bronze age, Dublin artisans continue to product exquisite celtic cross jewelry in a broad range. Designs include replicas of Ireland's most famous Celtic crosses including, the Cross of Moone, Celtic cross of Muiredach, Celtic cross of Scriptures, Celtic cross of Ardboe, Celtic cross of Durrow and the Celtic Cross of Saitn Patrick. The hallmark stamp from the Irish Assay Office not only guarantees the quality of the metal but ensures a superior handmade Celtic Jewelry is actually made in Ireland. Always look for the hallmark stamp as a guarantee of authenticity.