Gemstone value of the stone. Some treatments are used widely because the resulting gem is stable, while others are not accepted most commonly because the gem color is unstable and may revert to the original tone. Heat can improve gemstone color or clarity. The heating process has been well known to gem miners and cutters for centuries, and in many stone types heating is a common practice. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in “ametrine” – a stone partly amethyst and partly citrine. Aquamarine is often heated to remove yellow tones, or
Archibald Robertson (bishop) April) 1903, consecrated (ordained) as a bishop on 1 May (by Randall Davidson, Archbishop of Canterbury, at St Paul's Cathedral) and enthroned and installed at Exeter Cathedral on 5 May; he legally took up the See upon the confirmation of his election, which took place between his election and consecration (i.e. during April 1903). In 1912 Lollards Tower on the Exeter City Wall was rebuilt and several sculpted stone tablets displaying the arms of Bishop Robertson were set into the walls, including one over the arched entrance known as Bishop Carey's Postern. He served as diocesan bishop until 1916, when