Care of the Reference Materials

The blocks are supplied in a velvet lined case to 
protect the fine surface finish produced at manufacture. Providing that they are handled with care （cotton gloves are recommended） and always stored in the case 
provided, they should give many years of satisfactory service. Exposure to organic solvents can cause severe fogging of the surface and must be avoided, as should any attempt to clean the block with abrasive cleaners.

In the event of the surface of a block becoming soiled, it should be immersed in dilute neutral detergent solution which may be warmed to 40°. Low power ultrasonic vibration may also be used to remove the contamination. It should then be rinsed thoroughly with deionized water and dried carefully with a soft lint-free cloth.

Recorded Spectra

The following spectra were recorded in the ratio 
mode, using a Perkin Elmer LS50B Luminescence Spectrometer. The spectral band width for both 
excitation and emission monochromators, was 2.5 nm. Data points were recorded at 0.5 nm intervals. These spectra are specific to this instrument and the operating conditions used. Other instruments, or different 
operating conditions will produce spectra with maxima which may vary both in terms of relative magnitude and wavelength.

The corrected Spectra were recorded using a Perkin Elmer MPF44-B and should relate to others recorded in a similar manner.