This part of DIN 13991 describes requirements for toothlike colour embodiments made from ceramic materials, hereinafter referred to as colour rings, used to determine the tooth colour within the patient's mouth or to check the colour of a dental prosthesis. This standard does not cover the coordinates of tooth colours within the colour space (colour coordinates) which can be optionally specified by manufacturers and characteristics, in particular the colour deviations of ceramic and other masses or materials used for manufacturing dental prostheses. This standard does not cover means for colour visualization such as shade guides, for example material shade guides and colour patterns for certain ceramic and other masses. They can be manufactured from any material and serve exclusively for demonstration of the colour effect, they do not serve for colour determination of colour in the mouth. This standard has been prepared by Working Committee NA 014-00-00-07 AA "Keramiken" ("Ceramics") at NA 014-00-17 AA "Metalle" ("Metals") at NADENT.