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GBV9972 (9% Au containing precious metal paste)
PBV20012 (Bright indirect screen-printing palladium)
Johnson Matthey (now Fenzi AGT) is the market leading manufacturer of precious metal inks in the world and Teka Color is the distributor of Johnson Matthey (now Fenzi AGT) precious metal products.
These products are highly viscous pastes that are specifically designed for indirect screen printing on the glass substrate that fire as a bright mirror-like reflective film. The products contain precious metal compounds (Gold, Silver, Palladium, Platinum) in combination with a mixture of resins and solvents.
Application
Diluting this range of lusters are not recommended however if the paste starts to dry, up to 5% T 62 diluent can be added to compensate the evaporated solvents.
These products can be applied by polyester screen at a range of thicknesses, although trials should be carried out to establish the weight range, mesh size of 120 and 130 are recommended. The thickness of the precious metal applied is critical in achieving satisfactory and economical results.
Reasonable precautions should be taken to keep both wares to be decorated and the liquid precious metal as free from dust as possible. Once applied, the product can be left to dry naturally or force dried. Dust settling on the wet film can give rise to pinholes and blemishes; therefore, the freshly decorated pieces should be protected until dry.
Firing
Firing conditions are as important as good application. Good results can be obtained with most types of kilns using either gas or electricity. The kiln should be well ventilated to ensure the maintenance of an oxidizing atmosphere, particularly during the early stages of firing 250-400°C (482-752 F), at which temperature the gold film first displays a metallic appearance. Sudden changes in temperature should be avoided. The temperature should be raised steadily to the maximum required and held at peak for at least 10 minutes.
Peak temperatures of 470 to 600°C (878-1112 F) can be used depending on the type of kiln, the quantity, size and shape of the ware, the softening point of the glaze and the duration of the firing cycle (typically 11⁄2 hours cold to cold). The higher the peak temperature can be set the better the durability of the decoration of the glass. Increasing the soak time (typically 15 minutes) also leads to better durability. This effect is strongest at low firing temperatures.
