08 February 2016
When we speak of the measurement of the colour of ink, the different forms and types of ink can all be included in similar measurement guidelines. The basic aspects of the appearance of ink can be analysed in both solid and liquid ink types.
Inks today have many different uses including use in printer cartridges, in artwork, for writing and even in tattoos. Despite the different uses, the colours should all be of a good quality and shouldn’t differ from batch to batch.
Why should we measure colour?
The very simple reality of producing ink is that the customer is buying colour. Whether it is for use in a printer or in a work of art, colour is extremely important. Printer ink colours should be the same shades of black, cyan, yellow and magenta from printer to printer, time after time.
As an example, for a company that mass produces magazines, these are normally going to be laid out next to each other on shelving in a shop. If the ink is of even a slightly different colour, whether a different hue or too light or too dark, it will be instantly noticeable and reduces the perceived quality of the product being sold. If the colours dull from magazine to magazine, they will not be as vibrant on the shelves and therefore not as appealing to a customer. Consistency and quality are key with a product that is so dependent on its colour.
What data are we looking to receive?
If the analysis is to be of either the reflected or transmitted colour, values in colour scales such as CIE L*a*b* or Hunter Lab can give a numerically detailed depiction of the actual colour of the ink. This data can give an extra degree of accuracy when deciding if the product is of sufficient quality to be sold.
Ideally, a good method of practice to use would be to gather numerical data from a perfected sample to create what is known as standard data. All future samples will then be compared to this standard. The resulting data can be portrayed as both absolute values or as difference values, showing the variation (if any) between the sample and the standard.
The dECMC index is another very helpful index to use when there is the possibility of a difference between a standard and a sample. Delta ECMC is an elliptical tolerance that correlates well with the differences that a human observer notices and provides the difference as a single number.
What instrument is best to use?
For the application of appearance analysis of ink, an instrument should be used that is capable of measuring the type of ink produced but also has the option of versatility and can be used for even just one-off measurements of other samples.
As an example, the UltraScan VIS utilises diffuse/8˚ geometry with the option for measuring both reflected and transmitted colour of a sample, allowing for analysis of transparent, translucent and opaque samples. This instrument with a CIE-conforming sphere negates the effects of scattering normally found in transparent samples when taking transmission measurements in TTRAN Total Transmission mode.
With this instrument, sample cells filled with the liquid ink can be placed at either the reflectance port for opaque samples or in the transmission compartment for translucent or transparent samples. Singular or multiple measurements can then be taken depending on internal methodology but, as a general rule, the more measurements taken, the more accurate the data can represent the batch as a whole.
Depending on the viscosity of the ink, a flow-through cell could be used to take readings of a large amount of the sample. This cell works in conjunction with a peristaltic pump that feeds the sample through the cell for measurements and then out to ensure an average set of data that represents the entire batch.
If the ink samples are solid, they can be clamped to the reflectance port for analysis and either singular or multiple measurements taken of one sample or a group of samples representing the same batch.
Regardless of the physical state of the ink, colour and quality analysis can be an easy and cost-effective process that can vastly improve the quality of the end product whilst saving money by reducing waste or the need for extra additives.