nm dye concentrations tested ranged from 5 mg l to 25 mg l dyes 1 4 are readily visibly fluorescent at 5 mg l concentration at a high concentration 22 mg l no change in etch rate was observed with these dyes added to two separate commercial buffered oxide etchants nh 4 f hf solutions known to be most sensitive to minor formulation changes or impurities one of these commercial etchants contained 33 6 percent by weight nh 4 f and 7 8 percent by weight hf the other commercial etchant contained 39 percent by weight nh 4 f and 1 2 percent by weight hf mixtures of the dyes in these etchants were heated to 60 u00b0 c and cooled with no apparent loss of fluorescent intensity in the mixture the dyed etchant mixtures also show no loss of fluorescence after six months storage at 24 u00b0 c a series of etchant solutions containing 33 6 percent by weight nh 4 f and 7 8 percent by weight hf was made to test dyes in accordance with the present invention and the properties of the aqueous solutions containing the dyes the concentration of the dyes tested ranged from 5 milligrams to 25 milligrams per liter of corrosive fluoride solution it was found that solutions containing 7 hydroxy 4 methyl coumarin 7 amino 4 methyl coumarin 7 amino 4 trifluoromethyl coumarin or 7 amino 4 methyl 2 quinolinol were readily detectable to the naked eye when irradiated with low intensity ultra violet radiation using the commercial unit noted hereinabove when the dye concentration was as low as 5 milligrams per liter further tests were performed to.