Glass colour filters

One of the simplest tristimulus colorimeters is the Lovibond Tintometer. The apparatus consists essentially of a viewing tube and light reflected from a standard white surface. One half of the field is illuminated by the light reflected by, or transmitted through, the specimen under examination. The other half is illuminated directly by a beam of standard light. Into the path of the latter beam coloured glass filters of the subtractive primaries are inserted and moved by mechanical means. 

Fig. 2. A schematic drawing of the second harmonic imaging experiment and apparatus. KG-1 and 7-54 are coloured glass filters. The 266 nm signal follows the path through the 7-54 filter and the probe beam follows the path through the neutral density filters (ND)...

An important feature of interference filters is that the blocked light is refleeted back into the beam path. Beeause the filter is placed in a collimated beam, the reflected light is perfeetly foeused back into the sample. This can cause notieeable afterpulses in the IRF of a TCSPC system. The remedy is often to use an additional coloured glass filter in front of the interference filter. If the filter has an additional absorptive layer on one side, this side should be oriented toward the light souree. 

Fig.6.43. Examples of transmission curves for coloured-glass filters (Courtesy Schott Glaswerke)...

Absorption filters, in contrast to interference filters, can be used at any angle of incidence and can thus be used in strongly converging or diverging beams. It should be noted that certain coloured glass filters can exhibit rather strong broad-band fluorescence when used to block UV light, which... 

Filter the product at the pump, using an alkali-resisting filter-paper, or a sintered glass filter-funnel. Wash the crystals on the filter with a small quantity of ethanol to remove the purple colour, and then drain thoroughly. 

Pipette 25.0 mL of the bromide ion solution (0.01-0.02M) into a 400 mL beaker, add excess of dilute silver nitrate solution, filter off the precipitated silver bromide on a sintered glass filtering crucible, and wash it with cold water. Dissolve the precipitate in a warm solution prepared from 15 mL of concentrated ammonia solution, 15 mL of 1M ammonium chloride, and 0.3 g of potassium tetracyanonickelate. Dilute to 100-200 mL, add three drops of murexide indicator, and titrate with standard EDTA (0.01 M) (slowly near the end point) until the colour changes from yellow to violet. 

Light filters. Optical filters are used in colorimeters (absorptiometers) for isolating any desired spectral region. They consist of either thin films of gelatin containing different dyes or of coloured glass. 

Coloured glasses are used for decorative ware, as distinguishing marks on glass apparatus, as easily identifiable metal sealing glasses, and as light filters. 

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