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Mill addition for Aluminum Enamel to reduce bubbling

For Aluminum Enameling what should be the mill addition for the suspension of the frit? In our case, we do Aluminum Metallizing on the mild steel objects, whereby you get a rough finish of Aluminum of about 50 to 80 microns; this is then coated with the aluminum enamel. Our problem starts when the coating is left to dry before firing, this water based application before getting fully dried develops very tiny bubbles all over. Is this because the metallized Aluminum reacts with our mill additions? cause for suspension of the milled frit we use about 2.5% of Boric Acid, 2.5% of Potassium Hydroxide, 0.5% of sodium silicate and 0.5% of Sodium nitrate and 1% of borax.

Are these the only suspending agents for Aluminum Enamel or should we try some thing else? are we using more of Potassium Hydroxide? or is the Boric Acid giving us the problem? can any one doing Aluminum Enameling specially on metallized surface help? We will be grateful.

Tanvir Bharucha
an enamel works - Mumbai, Maharashtra, India
2003

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Your mill addition is probably too reactive. Try reducing the amount of KOH.

Best regards, Charles

Charles Baldwin
frit supplier - Cleveland, Ohio
2003