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Burnishing is a surface marking technique  intended for coated metals - usually lacquered brass - where the coating  is removed to expose the bare metal. It is a method of rotary engraving on  metals that tends to bridge the gap between diamond drag (scratch  engraving) and routing. The biggest advantage of burnishing is that it  enables the engraver to produce wider line widths than are obtainable with  a diamond graver without having to cut deeply into the metal. Burnishers  can be used with single and multiple line fonts, and are excellent for  producing detailed line and logo work on metal. Burnishing offers the  ability to create enhanced effects on both lettering and graphics and is  relatively simple process.

The most  common application is on the brass plates on trophies and plaques. This  "trophy brass" is a relatively hard material that yields excellent  burnishing results. It is available in various gold tones with clear or  colored lacquer coatings. When burnishing the gold material, the lacquer  is removed exposing the bare metal. The burnished areas can then be  oxidized or blackened resulting in a gold plate with contrasting black  letters. (See "Color Filling Fact Sheet"). When burnishing the colored  materials, the result is a colored plate with contrasting gold letters  without the need for further treatment.

Burnishing can also be done  on materials other than brass. However, much of the success or failure  depends on the hardness of the material. Since burnishing is a surface  marking technique, it is critical that the tip of the burnishing tool does  not penetrate the surface of the material by an appreciable amount. Hard  materials tend to prevent deep penetration of the burnisher forcing the  tool to work on the surface as it was designed. However, on softer  materials the tool is able to penetrate deeper and can produce ragged  edges and unacceptable results. Many of the colored aluminum products on  the market fall into this category and are not ideal choices for  burnishing although some can be burnished effectively using a diamond  burnisher. There are also harder aluminum products available with clear or  black anodize treatments that can be effectively burnished.

It is  also possible to burnish metals such as steel and stainless steel. Since  the burnishing tool produces a swirled pattern, the mark is visible and  may be suitable for some marking applications not requiring a sharp, well  defined character. Generally speaking, however, these metals do not have  coatings and therefore, the burnishing can not be blackened to add  contrast.

Burnishing Tools
The tool used for  burnishing is called a "burnisher" which is a rotating tool that is used  in a motorized spindle. It is usually a carbide or carbide-tipped tool  that is ground with four facets. Two of the facets form an angled chisel  edge on the center of the tool. The other two facets are ground  perpendicular to the chisel edge, equidistant from the center of the tool  and determine the width of the tip. Antares carbide burnishers are  available in widths from .005" up to the full diameter of the tool in  increments of .005" (.005", .010", .015", etc.).

(Carbide Burnisher)

Burnishers can also be made as diamond-tipped  tools (diamond burnishers or rotating diamonds) similar to those used in  glass engraving. These tools produce a more brilliant effect and have a  longer life, but are considerably more expensive. Diamond burnishers are  standardly available in tip sizes of .005", .010", .015", .020" and .030".  Larger sizes are available as special orders.

(Diamond Burnisher or Rotating Diamond)

When selecting a tip size, follow the same guidelines  that are used for standard engraving cutters. For example, if you were to  use a .030" cutter when engraving plastic, you would use a .030" burnisher  when burnishing a brass plate with the same font and letter size. Since  burnishing is generally done with small, multiple-line fonts, the most  common tip sizes are between .005" and .030".

Burnishers are quite  durable and are capable of producing thousands of characters. Like  cutters, they do become dull, however, and require periodic resharpening.  As a burnisher dulls, the chisel edge becomes rounded. This produces rough  edges and if allowed to continue, will result in the surface coating being  smeared in to the burnished stroke and can hamper  oxidizing.

Since the purpose of  burnishing is to remove the coating from the surface a the material, the  key to achieving successful results lies in the amount of downward  pressure that is exerted on the tool. A burnishing tool is not a cutter  and if too much pressure is applied, the tool will be forced into the  material resulting in a rough, ragged stroke. Ideally, the tip of the tool  should "float" over the surface with only enough pressure to remove the  coating without digging into the metal.

To set the machine for  burnishing, remove the depth nose and lower the spindle to its down  position. Next, screw the knob into the spindle, slide the burnisher down  through the knob until the tip contacts the plate and then tighten the set  screw in the knob. Raise the spindle and then increase the "depth" a few  thousandths of an inch by either adjusting the down stop on the spindle or  sliding the burnisher further through the knob. Since the bases and tables  of all machines are not perfectly level and material thickness can vary,  it is important to set the tool at the lowest point on the plate. This  will ensure that the tip of the tool will remain in contact with the  entire surface of the plate.

On computerized machines where the  Z-axis (up and down) is controlled by air and spring pressure, both should  be set to their lowest setting. The motor speed should be relatively fast  and the engraving speed should be at about the middle of its range. A  slower engraving speed will produce a smoother finish in the burnished  stroke.

The set-up procedure is identical for both pantographs and  computerized engraving machines, however on a pantograph the correct  pressure is determined by the "touch" of the operator. It is a technique  that is easy to develop and the results should be equally as good as those  achieved on a computer. One trick that some pantograph operators use is to  remove the spindle return spring. This allows the spindle to drop on its  own and float over the material. The weight of the spindle alone is  sufficient to produce the desired results, but you must remember to lift  the spindle when moving from character to character.

One way to  simplify the burnishing process and achieve consistent results is through  the use of a spring loaded burnishing attachment. These devices are used  in place of the conventional knob and have an internal spring that applies  the correct amount of pressure. These attachments usually require a  burnisher that is longer than normal, so be sure to specify that you are  using one of these attachments when ordering to ensure you get the proper  length tool.

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