Bronze Patina Basics by Mark Parmenter There are always questions about patinas on the various lists I monitor and I thought I'd offer some basic information on patinas to my visitors.  It is not rocket science, but there are some basic rules that provide guidance to the novice patineur.  I am going to address some general guidelines to the art. There are 3 basic types of patinas; hot, cold and buried.  Hot patinas are applied to a hot bronze surface by brush or spray.  Cold patinas are applied to a room temperature bronze by spray, brush or dipping into a solution.   Buried patinas are made by applying a patina solution to a bronze wrapped in a sealed container and left to slowly color.  Hot is fastest and most controlled, cold takes stronger chemicals and is less controlled, buried takes days to weeks and is uncontrolled for the most part.  I will discuss hot patinas, which are the most widely used for the patination of art work.  There are also pre-made patina solutions that work very well.  I will give three formulas that I use most, but there are hundreds of others listed in the various books about patinas.  Most are useless for general work, but there are still many that are good in various situations.  A short list of equipment for patina work,includes: Chemicals to make solutions.  Distilled water, always use distilled water to mix patina solutions.  Plastic mixing containers.  A scale if possible. A heat source, usually a roofer's torch, propane torch or heat gun.   Temperatures are going to be over 100C, so you need some serious heat. Spray bottles and brushes WITH PLASTIC FERRULES.  I use basting brushes from the cook's store. Good ventilation.  Most of these chemicals are very nasty. Hand, eye and respiratory protection. A heat proof stand upon which to place your work.  A lazy susan is also handy. Cleaning and rubbing supplies.  Good detergent, solvents, Scotchbrite pads, Bon Ami scouring powder, paper and cotton towels. Wax.  Johnsons Paste wax or Moser's paste wax.  (From Woodworker's Supply) Very basic patina formulas:  With three chemicals, you can get most of the traditional colors for patination.  Used in combination, many colors can be achieved. Ferric Nitrate-golds-browns-reds. Medium solution.  1/2 teaspoon in 8 oz. water.  Apply hot with spray or brush. Cupric Nitrate-greens-blues.  Medium solution.  2 teaspoons in 8 oz. water.  Apply hot with spray or brush. Liver of Sulfur (sulphurated potash) gold-brown-black- 1/2= teaspoon in 8 oz. water.  Apply hot with spray or brush. Birchwood-Casey M-20-gold-browns,black-as directed.  Apply cold.  Make up all solutions before you start.  All but liver of sulfur can be kept indefinitely. 1.  The surface must be clean.   By clean I mean all oils and oxidation need to be removed.  The most frequent oils are oils from your hands so do not touch the surface with bare hands.  Use rubber gloves during wash and subsequent handling..  We clean the surface by bead-blasting immediately before patina.  Other methods include a good detergent wash in water and thorough rinsing then wiping with a solvent.  We use methyl alcohol.  Rubbing with Scotchbrite pads during washing helps improve the surface for patina and helps remove oxidation.   Dry with compressed air, clean towels and/or a hairdryer.  Patina within 1/2 hour. 2. Apply a base coat.  Most base coats are liver of sulfur or Birchwood-Casey M-20.  These can be applied either hot or cold.  I apply liver of sulfur hot and B-C M20 cold.  Use spray or brush to desired color.  A good solution for liver of sulfur is a lump of Liver of sulfur about the size of the end of your thumb to 1/2 gallon of DISTILLED water.  Make this solution new every time you use it.  After applying the base coat, rub the patina under running water with Scotchbrite pads and/or scouring powder and rags.  This should be done carefully to avoid taking off too much patina on the high spots, your call.  this step gives depth to the patina.    Rinse well and dry.  Don't touch the surface with bare hands.  You could just stop here for a traditional brown patina.  Just heat it up and wax. 3. Apply patina coats.  Patinas are usually a series of washes applied to the hot surface.  The color you achieve is dependant on the temperature of the metal, the composition and strength of the solution and application.  Heat the surface of the bronze slowly and evenly staring at the base. You will notice that the surface forms a watery sheen and then the water sheen will dissipate.  Keep heating.   The goal is to get and even heat in the section you are working.  Keep in mind that thick sections need more heat, thin sections take less heat but cool faster and that heat rises, so the top will probably need less heat.  Do not over heat or you will burn most patina solutions.  The correct temperature for a given color takes some experience, so keep at it and go slowly.  When the work is hot enough, in most cases, a drop of water will just bounce off the surface.  Start spraying and/or brushing on the solution evenly around the work.  Keep heating and applying until you get the color you want.  You can apply different solutions for different colors and layering effects and this is where the art comes in to play.  The color at this point will appear to be flat and saturated, this is not the final color after waxing.  The best way to see what the final waxed color will be is to wet the coating and observe what the color is while wet, just before the solution evaporates.  Experiment. 4. Apply wax while the work is still warm to seal the patina.  Re-wax when completely cool and buff. Two good books on patinas are Patrick Kippers "Patinas for Silicon Bronze", 1995, Rogers and Wilson Publishing. and Ron Young's "Contemporary Patination" Sculpt Nouveau.  I suggest you buy one for a detailed description of patinas and patina application. Source for chemicals: Bryant Labs, 800-367-3141; Birchwood-Casey, 612-937-7931 Sculpt Nouveau, 800-728-5787 (pre-mixed solutions and dyes)
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