Spectrophotometer nightmare: comments and reactions
Our article caused some stir in the industry. And that was our intention: we wanted to create awareness on the issues, we didn’t want to ‘condemn’ the vendors of spectrophotometers (otherwise we would have mentioned names). And yes, we did use a strong headline to draw attention... (the goal justified the means, at least in our opinion).
Spectrophotometers are specialised tools, they need to be handled with care and with the appropriate knowledge. With care, that means: maintain them well! E.g. regular maintenance by the vendor is a cost, but it really is necessary. With the appropriate knowledge, that means: know how to use them in the right way, know how to interpret measurements and set goals that can be measured undisputedly.
In the article, a few points have been updated, based on the input we got (btw: thanks to all who delivered input!). Below is some more information on other comments.
VIGC only did one measurement, they should have taken three measurements and averaged the results
Yes, we only did one measurement and we should have done three, to have a real scientific approach. But, how many printers or print buyers do it that way? We have chosen to test spectrophotometers in the same conditions as they are used in the industry. And most printers and print buyers just take one measurement... Which can be very dangerous! Several years ago, we did a test with a ‘cold’ spectrophotometer (first use on Monday morning in winter time): it took over 10 measurements before the results were more or less consistent!
The measured devices were within ISO-specifications for spectrophotometers.
Yes, indeed. And this brings us to the goal of our article: create awareness. Many customers are demanding tolerances that are tighter than the ISO-specifications for printing (ISO 12647). With a tolerance that is often lower than the inter instrument deviation that is allowed according to ISO specifications for spectrophotometers, you will get trouble. What if the print buyer specifies a target color in CIELAB and the measured color is outside the - small – tolerance, only due to the deviation of the device used? That would mean that a job that got rejected – with either a reprint or a price reduction – for the wrong reasons! That’s why we wanted to create awareness.
A company always uses the same device, so inter instrument deviations are not that important.
Not always the case! We can’t put a percentage on it, but certainly in the case where the print buyer also has a quality department, they will check – and approve or reject – the print job with another device, maybe even with another brand of spectrophotometer. So in that scenario, where both printer and print buyer check the colors of a job, according to a specified color (e.g. a brand color), inter instrument deviations can play a significant role. And we’ve seen this in real life: printer measures the job within specs, print buyer measures it and it is outside the specs... Job got rejected.
To conclude an anecdote to illustrate why we wanted to create awareness...
A few years ago we got contacted by a printer of corrugated boxes. He was in the running for a really large order, but the customer had set quality targets and he didn’t know what to do with them... The maximum delta E that the customer had specified, was – if my memory serves me well – a delta E of 3 (since they didn’t specify which delta E, we assumed it was delta E*ab). Now consider that this was on brown corrugated boxes... The substrate itself has color differences that exceed delta E of 10! It is covered with dark spots... The customer delivered a printed ink sample. However, this was printed with a hand roller, on a nice glossy extremely white paper... and that was the color reference for printing on brown corrugated. The ink sample itself was full of lighter and darker areas, so which color was the reference??? But in the end, a certain amount of boxes should be sent to the quality department of the print buyer. And they would measure it, with their device – which was a completely different type of spectrophotometer than we are using in the printing industry - and approve or reject the print job... This is just a way to be sure to find a reason to reject jobs and demand a discount... This is not about getting the colors right anymore.
Color is something really complex and you need the right skills, the right equipment to get the colors right, to measure them in the right way.