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Description
Color filling is a term used within the awards and
engraving industry to describe a variety of techniques used to
add color or contrast to engraving. Even though there are a wide
variety of engraving materials available in a multitude of colors,
thicknesses, and finishes, there are often times when it is desirable
to color the engraving to make it stand out or enhance the overall
appearance of the product.
Oxidizing
There are three basic processes or applications that
fall under the category of color filling. The most common, which
is used to blacken engraving on brass and aluminum is actually
an oxidation process done with a mild acid that blackens the exposed
metal upon contact. Since this oxidizing process isn't selective
as to where it works, it can only be used on metals that have
some kind of coating that is removed in the engraving process.
For example, the commercially prepared brass common to the industry
is coated with lacquer or some other durable finish. Aluminum
can be coated in a similar manner, or it can be anodized. Anodizing
is an electro-chemical process that seals the surface of the metal
and prevents natural oxidation. When we remove any of these finishes
with a diamond graver, burnisher, or a rotary cutter, the exposed
areas can be blackened with the oxidation solution without having
it affect the rest of the plate.
Oxidizers are available for both brass and aluminum. They are
reasonably effective and the only consideration is that it is
fresh and free of contaminants. While most oxidizers are supplied
with a dauber, this may not be the best way to apply it since
you would be continuously putting the dirty applicator back in
the solution. A better method is to use cotton swabs and discard
them after each use. It is equally important that the engraving
be clean and free of any oil or even fingerprints. Since the bare
metal goes through a natural oxidation when it is exposed to the
air, it is a good idea to oxidize it soon after it is engraved
so the full effect of the oxidizer is achieved.
Apply the oxidizer liberally to all of the engraving. It sometimes
helps to actually "scrub" it into the letters with the
swab. Allow the engraving to darken and when the desired effect
is achieved, rinse the plate with water. Rinsing will dilute the
acid and stop the oxidation process. If the oxidizer is left on
too long, the process will continue and the blackened areas may
turn gray and chalky and even flake out of the engraving.
After rinsing, blot the plate softly with a cloth or paper towel
- don't wipe it because it is possible to rub the black out of
the letters. You can make a final clean-up after the plate has
dried. If there are any areas that didn't take, you can go back
and repeat the process. Oxidized engraving tends to have a dull,
lusterless appearance. It is possible to enhance the appearance
by applying silicones, spray lubricants, or even furniture polish
to the plate but while these methods tend to darken and add gloss
to the lettering, their effects usually diminish in a relatively
short time.
Paint Stick
Actual color filling where a fill material is applied
into the engraving can only be done on rotary engraved plates
with sufficient depth and is usually done with paint or a paint
stick. A paint stick looks like a large crayon, is available in
a variety of colors, and is simple to use.
First, shave the end of the stick with a knife or razor blade
to remove any skin that has formed. Next, rub the stick back and
forth across the engraving until the letters are filled, and then
wipe off the excess with a cloth or paper towel. On some surfaces,
the paint stick will leave an oily residue that can stain the
surface of the plate. Sometimes alcohol or paint thinner is effective
in removing this film, but the easiest way to completely clean
the template is to allow it to dry overnight and then wash it
using warm water and a non-abrasive cleaner. While this method
of filling is easy and reasonably durable, it never gets completely
hard and doesn't offer the smooth, glossy appearance that paint
does.
Paint Filling
Paint filling, while a little more difficult than other
methods, offers the broadest number of options in terms of materials,
colors, and applications. For metals and rigid plastics (phenolics
and acrylics), it is best to use a fast-drying, oil based enamel
to fill and mineral spirits for the cleaning operation. On soft
plastics such as flexible engraving stock and other materials
that may be affected by caustic solvents, use latex or acrylic
paints and water or alcohol for clean-up. Other than this, the
procedure essentially the same for both. In addition to the paint,
all that's required is an inexpensive brush, an old phone book,
and some pieces of stiff paper or cardboard (about the size and
weight of a business card).
The engraving should be smooth, free of burrs, and have sufficient
depth to hold the paint. As a rule of thumb, with characters up
to 1/4" high, engrave to a depth of .010" - .012".
On larger characters, it is advisable to go .015" - .020"
deep depending on the line width and filling technique used.
The paint should be thick enough so that it does not allow the
cutter marks to show through after it has dried. Using the brush,
apply the paint liberally so that the engraving is completely
filled. Immediately after filling, hold one edge of the cardboard
so that its straight edge rests against the plate and scrape off
the excess paint leaving just a thin film. Allow the plate to
dry for several minutes until the paint has started to set-up
and the surface can be wiped without disturbing the paint in the
engraving. The time varies depending on the paint being used,
but 5-10 minutes would be a good starting point.
The next step is the initial clean up of the surface of the plate.
Wrap two or three thicknesses of a lint-free cloth tightly around
a wood or plastic block and dampen it with thinner. Wipe the surface
of the plate lightly, in one direction, until the paint residue
is removed. On small plates, an easier method of cleaning is to
wipe the plate across the cloth. A widely used and effective alternative
to the cloth method is to use pages from a telephone book. Their
texture allows them to absorb the thinner, and any problem with
lint is virtually eliminated.
There are two key things to remember that can mean the difference
between success and failure. One is not to use too much thinner.
If the cloth or paper is too wet, thinner will seep into the engraving
and attack the paint, ruining the appearance. Secondly, when wiping,
do it lightly to prevent the cloth from coming in contact with
the paint in the characters.
After the plate has been wiped clean, there may still be haze
that requires some additional cleaning. It is best to allow the
plate to dry, preferably overnight, and then to do the final clean-up
when the paint in the characters has completely set. You may want
to use soap and water or a cleaner that will remove any oily residue
left by the paint and thinner.
When filling larger letters, it is possible to eliminate most,
if not all, of the cleaning and wiping by using an applicator
that allows you to apply the paint directly into the engraving.
Some systems utilize small plastic squeeze bottles with needle-like
nozzles while others are more elaborate mechanical dispensing
systems. With either method, paint is squeezed through the fine
nozzle directly into the engraved character. With a little practice,
it's easy to become adept enough to eliminate the need for major
clean-up.
Some of the best sources for small amounts of paint in a rainbow
of colors are touch-up paint from the automotive store, and paint
sold at hobby and art supply stores. Always test the paint before
applying it to your finished engraving to make sure it will not
effect the plastic.
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Step 2: Scrape off excess paint with card stock. | Step 3: Wipe clean with block wrapped with cloth dampened with thinner. |
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