 Another reason sometimes given to justify this rule is that it was difficult to paint with enamel (colour) over enamel, or with metal over metal.The rule of tincture does not apply to furs, nor to charges blazoned "proper" (displayed in their natural colour, which need not be a normal heraldic tincture).The blazoning of a charge "proper" can therefore be used as a loophole when its natural coloration equates to or approaches another heraldic tincture it is desired to overlie.