abstract |
Compounds from the class consisting of the phthalocyanines, naphthalocyanines, the aminium compounds of aromatic amines, the methine dyes or the azulenesquaric acid dyes, which have their absorption maximum in the range from 600 to 1,200 nm and a fluorescence maximum in the range from 620 to 1,200 nm, are used as crack-detecting agents. |