materials testing | Colour monitoring
work with them on standardizing best practices. This includes performing round-robin comparative measurements with multiple sites and customers that includes typical samples and a performance qualification (PQ) qualifying tile of a colour similar
to your products.” Instrument profiling software is regularly used to correlate a group of spectrophotometers to ensure
Variable’s Node+Chroma is a portable, wireless tool for communi- cating colour
current ASTM standards for colour retention of plastic siding, ASTM D6864 (for solid colours) and D7251 (for variegated colours) that used the Hunter scale, notes Dave Johnston, senior technical director at the VSI. “CIE L*,a*,b* colour space is considered to better
represent human colour perception and offers some advantages for the process of evaluating acceptability of colour change,” explains Johnston. “The Hunter-based systems required different types of siding colours (such as “medium blue” or “light green”) to be separated into distinct colour regions, each with its own boundaries and equation for evaluating colour change. The CIE L*, a*, b* system allowed us to find an equation that worked for all colours, both solid and variegated, and eliminate separate colour regions. This will greatly simplify the process of setting up and evaluating studies of colour change due to weathering.” The VSI is in the process of transitioning its colour retention certification programs from the old standards to the new one.
Some advocate the use of newer measurement algorithms, such as CMC, CIE94 or DE2000, but there has been only a slow movement towards their use. “The industry is extremely slow to move because it has a large amount of historical data and is reluctant to move to a new measurement system with different pass/fail tolerances,” comments Ron Beck, R&D manager at Americhem.
Calibrating, profiling, and ensuring consistency In addition to using the same units for reporting, instruments must be calibrated and qualified for accurately communicating colour and ensuring that col- our data is consistent from one instrument to another at multiple production plants around the world or throughout the supply chain. Calibration is standardized using CIE 15:2004 “Colorimetry” and auxiliary ASTM/ ISO and JIS colorimetric methods, notes Leggett. The larger concern, he adds, is a company’s standard operating procedures (SOP) for measurement. “It is important to verify the repeatability of your measure- ment made using your SOP. You should communicate your SOP measurement method to your customers and
38 COMPOUNDING WORLD | July 2014
consistent readings among the group. “Although all spectrophotometers read colour accurately when they leave the factory, there are variations among manufac- turers,” explains CyberChrome’s Becker. “Instruments also drift and change as they are used in the often dusty and dirty environment of a compounding facility. Profiling is used to correlate the readings of a fleet of instruments that are used together in the real world”. In addition to calibrating and profiling, a disciplined
programme of instrument monitoring is needed to ensure that an individual instrument’s colour readings are correct, she says. CyberChrome introduced Instrument Performance software, available as a stand-alone program or as part of its OnColor suite of software, to check and monitor the performance of a spectrophotometer to see that it is measuring colour consistently and accurately. “The test uses a set of long-term stable ceramic tiles that are measured on a weekly or monthly basis,” explains Becker. “The software tracks the readings to assess the consistency of the measurements and saves the data into a database so that it can track and plot the variations in the readings. These trend charts and plots help diagnose when it’s time to re-profile the instrument or if it needs factory service and re-calibration.” Even with tools to help ensure good colour commu-
nication, there is room for physical improvement. “There needs to be improvement in colour communica- tion as it relates to correlation between objects, spectrophotometer measurements, printed materials and colours displayed on a computer screen,” says Americhem’s Beck. The profiling of monitors, printers and spectrophotometers has helped improve the correlation in colour communication, although spectro- photometer profiling software must create standard profiles that can be used by all colour software like printer and monitor profiles.
New tools to meet customer demands Another area for improvement is easier communication between designers and labs for colour matching. “Customers expect that a compounder or masterbatch producer can offer quick turnaround for custom colour matching and can match any colour that they can dream up,” says CyberChrome’s Becker. “It’s getting to the
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