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The colour of money - changing the pigment used in clay bricks

Clay Technology magazine
1 Feb 2008

The use of zinc oxide in the production of yellow surface colour pigments for clay bricks is a long established practice, but in 2005, the price of zinc oxide became a concern for pigment manufacturers, and the next year the increase affected brick makers. To understand the consequences, it is important to consider price levels and the volume of zinc oxide used to produce such products.

Costly colours

The price of high purity zinc oxide powder to pigment manufacturers during 2005 was £850-900/t. This was further influenced by logistical costs and the size of batches purchased. By the end of 2006, the price reached an average of £2,200 – more than double the average 2005 price. This was a result of the growing Chinese economy and subsequent rise in global demand for metal oxides.

Dependent upon the actual colour target, the amount of zinc oxide used in the colour formulation varies between 50-70%, and, in some minor cases, up to 80%. Taking the raw material cost increase into account, such a pigment would be subject to a price hike in the region of £650, and occasionally, in excess of £1,000. This resulted in quarterly price increases for zinc-based products in 2006.

Attempts to purchase materials from other sources were often wasted efforts, as the integrity of the material was at times unsatisfactory. Cheaper grades of zinc oxide, though suitable in pigmentation, can contain trace elements of lead and cadmium. Although these elements only exist in small amounts, it was decided that to use such materials would be a retrograde move. Furthermore, forward purchasing was employed to retain some price stability. This was a great risk because of the varying US dollar exchange rate and increasing stock levels of high value raw materials, which squeezed cash flow.

Stain removal

As a direct result, Castle Colours has fast-tracked a programme to reduce and, where possible, remove zinc oxide from yellow stain formulations. Laboratory phase trials of powder and liquid versions showed limited success, particularly in terms of the brightness of colour achieved. If not for the continuing increase in the cost of the zinc oxide material during this period, it would have been easy to sideline the project.

However, environmental concerns relating to zinc oxide were highlighted under the added pressures of the Registration, Evaluation, Authorisation and Restriction of Chemical substances (REACH) regulations. Customers expressed concern as to how the regulations would impact products.

Cash or carbon?

The decision was made to complete the project and provide customers with a choice of products. This was driven by the desire to offer the industry something new and the belief in its future success. Another key decision was made at this early stage when the company agreed that costs would not be considered in the laboratory phase and that the only target would be to achieve suitable colour. This was an informal decision that ensured the project did not fail at the outset. To constrain the laboratory with added cost pressures would have been wrong and this is a decision that will hold with future projects. However, it is also something of a contradiction, considering the project was initially driven by the impact of cost.

As with all schemes, there were phases of success and failure. After the initial trials, acceptable colour products were achieved. The next question was whether the trials translated into success in the field. The initial answer was no. The reasons for these failures were addressed and reformulated products with more focus on particular factory targets have been produced. One particular cause of failure was that during application, the powder pigments did not adhere as well to the clay body as their zinc-based predecessors. This was corrected using information gathered from methods employed by Castle Colours GmbH, Germany.

There are now zinc-free products that work and produce satisfactory colours thanks to the help of a small number of proactive brick factory managers. Products have been proven on both soft mud and extruded production plants. Stable prices and more environmentally friendly products – without the dead fish symbol – have been achieved.

As an added benefit, the formulation can be exploited to produce new ranges of temperature-stable products. These will not require calcination and will therefore have a lower carbon footprint during manufacture.


Further information:

Tim Clay, Sales Director, Castle Colours, Castle Works, Podmore Street, Burslem, Stoke on Trent, Staffordshire, ST6 2EZ, UK. Tel: +44 (0)1782 575990. Email: