Using various combinations of accurately graded coloured glasses in each of the colours red, yellow and blue (the basis of the Lovibond system) it is possible to match visually the colour of almost any sample. It is then a simple step to express the sample colour numerically in terms of Red, Yellow and Blue Lovibond units. This numerical specification is then given to Tintometer’s glass production department for manufacture of a glass filter of the required colour. This is then mounted in a Lovibond test disc, which holds a maximum of 9 individual filters, for use with the appropriate Lovibond comparator instrument. The numerical specification is retained, and copies can be supplied at any future time.
The following examples of orders for customised colour standards illustrate the extensive range of applications for this service:
Quality Control of Golden Syrup
The samples of syrup provided did not fall exactly onto a standard colour scale but, if they were dulled slightly using a pale red glass screen, then the sample colours became a good match with the Series 52 (Brown) scale. As a result we were able to supply the syrup manufacturer with a set of Series 52 discs (4/56A, 4/56/B and 4/56/C) modified to include a pale red glass centre screen in each disc to dull the samples.
Special Disc for Hydrocarbon in Water
This disc was made for an oil platform in the North Sea where it is being used as a visual back-up for measuring crude oil in sea water, a test usually carried out on an infrared spectrophotometer to ensure that water discharged to sea does not exceed the limit of 40 ppm hydrocarbons. The oil is extracted from the water sample using Freon forming a separate pale yellow layer, the colour of which can be used to determine the concentration of hydrocarbon in the sample. The yellow portion is run into a 40 mm cell and matched with the disc in a Comparator 2000 to give hydrocarbon concentrations in the range 10 - 100 ppm. As yet this disc has not been applied more widely but, in theory, it should be applicable to other hydrocarbons although we would need to verify the application of correction factors for different oil types.
Colour Grading of Contact Lenses
The need for a simple yet reasonably accurate method of colour grading this pale blue tint recently encouraged a manufacturer of plastic contact lenses to get in touch with Tintometer with their problem. As anyone who wears them will know, contact lenses are typically tinted a pale blue so that they can be more readily located when not in the eye. As a result we have developed a prototype colour grading unit consisting of three Lovibond blue glass filters mounted equidistantly on a circle of opal glass. The sample is placed on a glass screen in the centre which is also tinted to heighten the sample colour so that the filters used for grading have a more saturated colour and are therefore thicker and more robust . The filters are graded to represent the variation between the ideal blue tint and acceptable upper and lower colour limits. To grade the lens it is placed in the centre of the three filters and visually compared with them to establish if the lens colour is within tolerance.
Colour Grading of Blackcurrant Shandy
A brewer/bottler in the Far East wanted to monitor the colour of blackcurrant shandy. We were supplied with 9 samples of the drink, labelled 1 - 9, representing a range of product colours, with 5 being the ‘ideal’ colour. The blackcurrant samples were then matched in a 10 mm cell with Lovibond glasses. Because the customer was already using a Lovibond Comparator 3000 for EBC measurement, the customised filters were placed alternately in two Comparator 3000 discs: colour standards for samples 1, 3, 5, 7 and 9 in the left-hand disc with standards 2, 4, 6 and 8 in the right-hand disc.
Colour Grading of Sugar Solutions
We were asked if we could ‘replicate’ a simple colour comparator for grading of sugar solutions. The comparator consisted of four coloured glass rectangles fitted into a perspex box with adjacent viewing compartments. The sample in a bottle was placed in a compartment and visually graded by comparison with the glass colour standards.
Because the diameter of the sample bottles supplied was approximately 40 mm, the four glasses were matched using a sample path length of 40 mm. As well as matching these glasses, which were graded as 0.5, 1, 2, and 3 units, were able to provide intermediate values of 0, 0.25, 0.75, 1.5, 2.5, making a range of 9 colour standards. These were then placed in a test disc for use with the Comparator 2000+.
Dye Concentration in Wood Preservative
We produced a special disc for a UK-based manufacturer of timber treatment products, allowing them to assess the concentration of dye added to wood preservative during production. We prepared six samples representing varying strengths of the brown dye added to a 3% solution of the wood preservative. These were then matched with Lovibond glasses in a 2.5 mm cell.
Assessing Transformer Oil Condition
An R&D centre for power technology wanted to use the colour of transformer oil as an indicative measure of oil condition. We were supplied with eight oil samples, representing the range of colours over which they wished to grade. These samples were initially assessed for conformance with the ASTM Colour scale for petroleum oils and fuels. Although there was a reasonably good match at the lower end, the darker samples were too dark to allow use of this standard colour scale. We therefore decided to produce a customised disc containing filters matched to the eight oil samples in a 13.5 mm cell.
Special Colorimetric Discs for Plating Industry
Tintometer recently matched a pair of special discs for a customer involved in the electroless plating of plastic components. The discs used with the Comparator 2000+ allow direct measurement of the strength of palladium, which is used as a catalyst in the process.
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