Yellowness

So you’re a paint producer, or an adhesive producer, or you produce paper, inks, soap or ceramics, or maybe even you are a producer of a mineral like kaolin – and your customer brings up that dreaded YELLOWNESS objection: ”Your product has a yellow undertone”.  What can you do about it?

If you don’t do anything, he is quite likely to swap to the competitor’s product and there goes that customer out the window. They say that it costs much more to land a customer than to retain a customer, and the costs and effort to get a customer back once you have lost them must be even higher since you have to get their confidence back. Not an easy task.

Well, I don’t claim to have all the answers – I am sure you have lots of ideas on how to tackle this one – but I thought I’d tell you the story about how we addressed just such a problem, with very pleasing results. We approached it this way:

1. We measured where we were and where we wanted to be

Since we measure colour parameters all the time as part of our quality-control programme, we have a Lorentzen and Wettre Elrepho spectrophotometer in our QC lab which not only measures whiteness but also measures the full colour spectrum (L, a, b values). So when we were thrown the yellowness curved-ball, we first had to measure how yellow the kaolin actually was and compare it with the yellowness of the competitor that we wanted to match. This meant measuring the “b-value” which gives a reading on the b-axis or the yellow/blue scale, as shown on this schematic diagram:

So to find out what we were starting with, we checked the b-values of our product and the competitor and found the following:

The b-values confirmed that yes, indeed, our Filler Grade kaolin was more yellow than the competitor since a more positive reading on the b-axis means a more yellow colour.

2. We added a dye to get to where we wanted to be

The opposite of yellow is blue, so we thought, let’s try adding a blue dye to bring the kaolin’s yellowness down the yellow scale and more towards the blue end of the axis.

It sounds easy enough, but it involved a lot of lab test work on many different dyes because some dyes can also move your product’s colour along the red/green axis and we did not want kaolin with a pink or green tinge to it. Some dyes are not stable over time or over a broad pH range, so these factors also had to be taken into account. Finally we settled on a specific blend of a blue plus a bit of violet dye that gave us the desired result. This allowed us to create a new grade of kaolin, which we called PREMIUM GRADE. 

We set the specifications for the new grade to say that the b-value must be less than 3, so as to ensure a consistent colour for every batch. We found that the addition of the dye depressed the reflectance very slightly from 83 to 82%, which was to be expected, but it was still good enough against the competitor. Interestingly enough, we did not discontinue Filler Grade since some clients would rather play around with colour adjustment themselves instead of us doing it, so we still supply the original Filler Grade to those who prefer it.

So that is the story of how we used a chameleon’s trick to match the competitor, create a new grade of kaolin and meet the customer’s needs. We were able to make that desirable “drop-in” replacement that the customer was looking for. (Regrettably, this does not work for ceramic applications where the kaolin gets fired at high temperature, which would destroy the azo dye. These customers rather use our Ceramic Grade which has a lower iron oxide content. This helps to reduce the yellowness of the final fired article).

Note: If you are having trouble with the yellowness of a specific filler and you do not have your own Elrepho spectrophotometer, we would be happy to measure its L, a and b-values on our instrument and report them back to you.

Happy colour matching. For your filler requirements, please contact me in Cape Town. 

To find out more about the L & W Elrepho Spectrophotometer, look on their web site: www.lorentzen-wettre.com