Authenticating method

An improved method for authenticating an article comprising:

• (a) providing an article having authenticating display data thereon, said display data containing at least two photochromic compounds, the activated spectra of which photochromic compounds exhibit different absorption maxima;
• (b) exposing authenticating display data on the article to a source of activating light that activates all of the photochromic compounds in said display data;
• (c) examining the display data with verifying means that identifies at least one characteristic property of the photochromic compounds comprising the display data;
• (d) exposing the activated photochromic compounds contained in the display data to bleaching means that inactivates less than all of the activated photochromic compounds;
• and
• (e) examining the display data of step (d) with verifying means that identifies at least one characteristic property of the resultant level of activation of the photochromic compounds comprising the display data, thereby to authenticate the article.

An improved method for authenticating an article comprising:

• (a) providing an article having authenticating display data thereon, said display data containing at least two photochromic compounds, the activated spectra of which photochromic compounds exhibit different absorption maxima;
• (b) exposing authenticating display data on the article to a source of activating light that activates all of the photochromic compounds in said display data;
• (c) examining the display data with verifying means that identifies at least one characteristic property of the photochromic compounds comprising the display data;
• (d) exposing activated photochromic compounds contained in the display data to bleaching means that inactivates all of the activated photochromic compounds;
• (e) exposing authenticating display data on the article to a source of activating light that activates at least one but less than all of the photochromic compounds comprising the display data;
• and
• (f) examining the display data of step (e) with verifying means that identifies at least one characteristic property of the resultant level of activation of the photochromic compounds comprising the display data, thereby to authenticate the article.