The present invention relates to inorganic particles comprising at least two chemical elements in a predefined and analytically identifiable ratio. These particles are used as a marking means incorporated into or applied onto any desired article. They provide a high security potential against counterfeiting...http://www.google.de/patents/US6200628?utm_source=gb-gplus-sharePatent US6200628 - Use of inorganic particles and method for making and identifying a substrate or an article
