Thursday, April 14, 2011

Polish and/or Patina?


Posted by Mary Ellin D'Agostino
Technical Advisor

When metal clays come out of the kiln, they still require a bit of work. Silver clays have a matte white surface (this is the natural color of the crystalline silver). Base metal clays may have beautiful or not so beautiful patinas and a matte surface. Generally, these surfaces scratch easily and are not stable. There are multiple ways to finish or polish your metal clay pieces. Deciding what method to use is a personal choice weighing aesthetics and costs.

You may opt to leave the out-of-the-kiln surface on your clay. If that works for you and the piece remains stable with use or handling, great! If not, you will want to either protect or polish the surface.

Patinas, while beautiful, are often not stable and the colors will change over time. Protecting them with some kind of coating has its own problems because the patina colors are created by reflected light. Adding a coating (wax, varnish, acrylic, urethane, etc.) changes the patina appearance because when light is transmitted through the coating it is refracted. This means the light is deflected and changes the angle it is hitting the metal surface. The light is then reflected back, but at a different angle and the color appears different than before the coating was applied. This process of refraction and reflection changes how the patina looks, which may be good or not so good.

The matte white surface of the silver clay scratches easily, attracts dirt and oils, and will not be satisfactory for long term wear or use unless it is located in a protected area and (probably) coated with something to protect it from dirt and grease. The good news is that coatings will not affect the color and this can be a good solution for keeping that matte white finish. The matte white surface diffuses light. If you want a metallic, mirror-like reflective surface, you need to polish further.

The least expensive method of finishing metal clay is hand finishing. There are a host of options, but the most common ones involve brushing the surface of the metal clay with a stainless steel or brass brush. Stainless steel is excellent for dry brushing. Brass is best used with a lubricant such as soapy water. The two metals give a slightly different result and the fineness of the bristles makes a difference in the finish. Brushing pushes the crystalline surface of the metal over and smooths it out. The finish you get from these is, not surprisingly, called a “brushed” finish. This surface gently reflects the light in a variety of directions. Many people like this finish on their pieces and stop there. You can also refine the brushed finish by using sanding pads, papers, steel wool, or different grades of brushes.

Burnishers come in many shapes and sizes, but are generally made from polished steel or stone. These are used to create a surface that is highly reflective. Burnishers work by applying pressure from a very smooth surface onto the metal, compressing the surface and causing a very uniform surface that reflects the light more like a mirror. Creating a smooth mirror finish with hand burnishing is very difficult, but sometimes the slight irregularity of a hand burnished surface is just what you are looking for.

If you don’t like or have difficulty using handheld tools or want a different look, you can use machines to polish for you. Rotary tools can be used with a wide variety of polishing points, wheels, or bristles and polishing compounds. These types of tools can assist you in hand polishing your pieces. Your attention and time is still required, but electricity relieves you of some of the muscle power required by hand tools.

For finishing many pieces or to free yourself from even more of the labor, you can choose to tumble polish your pieces. Metal clay pieces are usually tumbled with highly polished stainless steel shot. Rotary or vibratory finishers tumble or vibrate a container containing the tumbling media (shot) and soapy water or burnishing solution. As the media impact the jewelry pieces, they burnish the surface. This is essentially the same action as hand burnishing but because the action is more consistent, the resulting look is also different. Other tumbling media are used for different purposes and different results.

Magnetic finishers work by using electro-magnetic action to spin or agitate polished, magnetized, stainless steel pins in the burnishing solution. The result of this is a softer more brushed look to the polished metal. The pins used in a magnetic finisher are very tiny and excellent for getting into small crevices.

Burnishing solution needs to be changed frequently to avoid the dreaded black gunk (a dark, dirty deposit) getting on your jewelry. More on the tumbling process and cleaning in a later post!

Each finishing technique gives a different result and you may find you want to vary the technique used to suit each piece you make.

Happy finishing!

2 comments:

Lora Hart said...

What an excellent post Mary Ellin! It should be required reading for every student. And instructor too. I learned a few things this morning too.

Gristella said...

Terrific blog. I've often thought there should be a "set" of classes in the fine art of finishing and patinas. I agree with Lora in that this subject should be investigated thoroughly by students of Metal.