|HYDROFLUORIC ACID / MICA GLASS EMBOSSING PROCESS
By Rick Glawson (Thanks to Larry White for typing the instructions for this site)
This process causes a deep stippled emboss to glass (not the light frosted effect associated with hydrofluoric creams). This treatment has been used well over 100 years in England and in this country, where it is practiced to this day.
A NOTE OF WARNING: HYDROFLUORIC ACID DOES NOT INSTANTLY BURN AS OTHER CORROSIVES, BUT IT IS ABSORBED THROUGH THE SKIN AND ATTACKS THE BONE. IT WILL DILUTE THOROUGHLY WITH WATER SO WEAR GLOVES AND WASH UP AFTER EACH USAGE. THIS ACID CORRODES ONLY GLASS, SO KEEP YOUR DILUTED MIX IN PLASTIC CONTAINERS. READ AND FOLLOW SAFETY INFORMATION AND DOCUMENTATION SUPPLIED BY THE MANUFACTURERS.
PREPARING THE ACID MIX- You may buy the hydrofluoric acid in 1 pt. Bottles at Del Amo Chemical. It comes 48 to 52% pure and must be diluted to approx. 20% for usage. Mix in a plastic bottle, 2 parts acid to 3 parts distilled water and stir. As a safety factor you may use blue food coloring instead of the distilled water.
PREPARING THE GLASS- A vinyl resist is placed on the glass. (Scotchcal #3470 material is perfect, or any peelable vinyl film that leaves no residue). Proceed with cutting out the artwork or design. Leave the image to be etched in vinyl on the glass. Coat the vinyl and the glass with asphaltum varnish and let dry.(approx 10 min.). Weed out the vinyl mask in the design that will be etched. Protect the back side of the glass from acid vapors, which will fog the glass, with protective contact paper, vinyl, or a coat of asphaltum varnish. You may at this point add in any additional flourishes or scroll working the open areas with a brush and asphaltum, allow to dry.
Choose the degree of stipple desired. A fine mica will produce a fine “hammered’ effect. Make a paste by mixing the mica (wet, but not runny) with your diluted acid in a plastic cup. Level the work piece in a well ventilated area and apply the paste evenly over the exposed areas. A wooden paint stick works fine.
The acid does not corrode the mica and in turn, the mica interrupts the action of the acid on the glass causing the a constant stipple. Allow the acid ½ hour on the glass. Remove the paste with the same application stick and put it back into your mica pot, being careful not to rub the fresh etched surface. The mica can be used repeatedly only refreshing with new acid. Rinse thoroughly under water. Remove asphaltum with thinner. Gild or silver as usual.