Our new Unleaded Enamel Range:

We now have available a range of unleaded, intermixable, dishwasher-durable and acid-resistant onglaze colours suitable for application on unleaded tableware glazes.

This new range has been developed by Lindsay Brindley and Roger Melville, the Managing Director and Technical Manager of ATC Colours. Both have more than 20 years experience in the development, production and quality control of ceramic colours and glazes, including pottery enamels. They have in their careers been involved in, or initiated the development of pottery and glass enamel ranges that are considered to be the market leaders in the industry.

Following the development and launch of the highly successful PE Range of lead-containing enamels, they turned their attention three years ago to the development of an unleaded range. Their goal was to provide unleaded enamels with as wide a firing range as possible in order to give colour stability and gloss over the wide variety of on-glaze firing cycles used today, from fast firing cycles of 60 minutes or less, cold to cold, to intermittent cycles lasting 5 hours or more.

In order to ensure that this goal was achieved the development was carried out in close collaboration with several major tableware producers in Europe, mainly bone china producers but also including some earthenware and hotel-ware manufacturers.

The result of this work is the ULE Range, which is based on a number of alkali-borosilicate frits, each made for a specific colour group but giving an intermixable range with a wide firing range. They have been fired successfully from 750 0C in an intermittent kiln to 930 0C in a fast fire cycle although the optimum firing cycle will depend on the glaze and body composition.

The range also includes enamels based on the Cadmium Sulphide/Selenide pigments, yellow, orange. mid-red, dark red and bright green, which have the same firing range as the other enamels.

The ULE range is technically lead free, and with the exception of the cadmium pigment based enamels, is also cadmium free. The lead content is less than 0.2%, typical analyses being less than 0.01%. Cadmium content, other than the exceptions, is less than 0.05%.

Chemical Durability

Dishwasher durability is tested by immersion in a 0.5% Calgonite solution at 78 0C, which is an accelerated alternative to 500 consecutive dishwasher cycles. The results show no appreciable deterioration of colour or gloss after 36 hours exposure.

Acid resistance is tested by immersion in 4% acetic acid solution at 22 0C for 24 hours in accordance DIN 51033 1986. Results are typically less than 0.05 mg Pd/dm 2 and 0.01 mg. Cd/dm 2.

With the exception of the Cobalt blues, there is normally no visible deterioration of colour or gloss in the acid test. In the case of the Cobalt blues the degree of acid attack is very dependent on the firing cycle, at some, higher, firing cycles the degree of attack is minimal. When required, an overprint flux is available to protect the blue enamel from attack. This flux is also compatible with the other enamels.

Work is continuing, and progress is being made, in improving the acid resistance of the cobalt blue enamels.

Keep watching this space.