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Epo-Grip How To
Cur's Ten Steps to Casting Better Fish Heads
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| Some
of the most frequently asked questions that arrive by email here at the
studio deal with the casting of fish and fish parts. Some are very
simple and some quite complex. Most deal largely with how to cast
the mouth details as well as the outside form of common fishes.
While
many mold materials may be used to construct a fish head mold, temporary
molds are always the better way to begin, since no casting made from a
life mold is perfect in all details. That conclusion having been
drawn, I prefer to make waste molds from alginate material and then
chase or correct the casting before spending the time and money to build
a Silicone RTV mold for production purposes. The preliminary
casting may be chased and corrected to perfection prior to molding in
RTV for multiple casting purposes.
Over
the past forty years, I have streamlined the materials, tools and
processes, until I have arrived at a technique which allows me to cast
the interior and exterior detail in a single mold, made by what I think
is a simple method. Here is that method, beginning with the tools
required for the job at hand: The first skill one begins to
acquire when casting an object is difficult for our human eyes and
vision center to develop. That is the ability to think in the
reverse, or in negative space terms. That is to look at a three
dimensional object and convert the shape into a space on the inside of a
mold. This ability to perceive form in reverse is necessary for
the planning of complex molds, in order to arrange the parting lines and
sections for the most optimum mold function and to insure release of air
from cast parts, while insuring delivery of the casting material to all
parts of the cavity. Fortunately, most fish heads are very simple
forms that can be interpreted by the novice. Some species having
spiny or turmerous projections on the head and opercular regions may
require special treatment, but most common species may be cast by this
method.
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Photo #1
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TOOL
LIST: Picture
#1
Scalpel Handle with straight, drop point blade....(I like the Bard-Parker
handles sold by Rio Grande Supply and the ribbed-backed Bard-parker
blades for this purpose.)
Alginate........The
Douglas and Sturgess, 45 minute cure product is best for ultimate
detail.
Store
the alginate in a refrigerator prior to use to chill the powder to allow
for longer work time.
Bent-nosed,
model-maker's pliers...........Used to break off dog teeth and other
mandibular teeth prior to molding.
Tape
measure or steel rule
Wide
bladed screwdriver or 1/2" dowel stock........For attaching a
"handle to the head"
Mixing
bowls............Three quart capacity for alginate and smaller container
for resin, Rubbermaid or Tupperware type
Cylindrical
mold container.......I prefer cheap ice tea or other beverage pitchers.
No matter what object is used, it must have straight sides for easy
release of the encapsulated head. One liter soda bottles may be
cut off at the shoulder for the purpose.
Cross
sticks or wire......... for suspension of the handle. I drill a
3/16 hole through the dowel and use a number ten wire to suspend the
head in the container. Two cross sticks will support a screwdriver
handle.
Serrated
Knife.......Or side cutters or snips for severing the head.
Spatulas.........For
mixing the alginate, and the resins.
Bowl
of ice water.........To use when mixing alginate to slow reaction times.
Ammonia.............To
clean and de-slime the fish head prior to casting.
Toothbrush...........To
assist cleaning the interior of the mouth and rear of head
Small
scraps of styrofoam...... For blocking the head into position prior to
freezing.
Toothpicks..........Or
soda straws for bracing the mouth, larger props for large fish.
Jeweler's
saw or coping saw.........For cutting the vent and sprue surplus from
the casting.
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Photo #2
Photo #3
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Separating,
preparing, molding and casting a fish head:
1.)
The head may be separated by several methods. I prefer beginning a
cut at the anterior end of the skull as illustrated in (Photo
#2)
and then continuing along the front edge of the gill brach membranes to
the ventral side of the fish at the juncture of the opercular
groups (Photo
#3).
This is done on both left and right side of the head, using the scalpel.
After the head is separated, clean it with ammonia by using the
toothbrush inside the mouth and to reach into recessed areas.
Clean well and then rinse in clean tap water, allow to drain for a bit
before continuing.
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Photo #4 |
2.)
Leave the gills attached to the thorax until after the head has been
severed at the atlas vertebrae, using the serrated knife, or a pair of
clippers or coping saw. (
Photo #4)
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3.)
If the gills are to be cast, they may be removed at this point by
cutting through the rear membrane adjacent to the scapular girdle and
removed as an intact group. (Not illustrated) The Gills may
be carded with Darico's "Foamies" and blocked and frozen in
position for molding at a later time. The cast gills may be fitted
to the head cavity by milling with a dremel tool until they fit in a
natural arrangement. when the fitting is complete, they may be
glued into place with thixo epoxie, such as Epo-Grip's Thixo adhesive
paste.
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Photo #5
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4.)
Using the bent-nosed pliers, break off the exposed teeth. A
cut-off wheel on a foredom or dremel tool may be used for large teeth.
Cut or break off the teeth just above the gum line. The stumps
will remain evident in the casting and will provide attachment points
later for artificially made teeth.
(Photo #5)
Attach the dowel or screwdriver handle. (Photo
#6.)
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Photo #6
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5.)
There are two principles to follow when casting any object: The
first principle common to all casting is the establishment of a delivery
system or tract through which the casting compounds may be
introduced into the mold cavity. These ducts or ports are called,
"Sprues". The second principle dictate deals with
releasing the air contained in the mold. As the casting material
enters the mold, the air must be allowed an escape path. The
escape ducts or ports are called, "Vents". Any mold, no
matter how simple or complex, must contain one or more material delivery
sprues and one or more vents to allow the escape of air or gases.
When devising this method of casting fish heads, I took a tip from the
ancient Chinese and designed the process so that a portion of the
casting, itself, (the operculae) became the vents that allowed for the
release of air as the casting material was poured.
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6.)
The sprue for the fish head casting is the screwdriver's shank in this
case, or a dowel which may be inserted into the brain cavity after
drilling a bore hole in the back of the skull to fit the dowel's
diameter. (Photo #6) During molding, the cavity left by the dowel or the
screwdriver becomes the mold's sprue hole through which resin is poured
to form the casting. The styrofoam block pinned between the
operculae provides a collection reservoir for excess resin and allows
the operculae to function as vents through which air escapes and the
resin rises to form the thin parts. The styrofoam block should
extend a bit past the tips of the operculae to allow a measure for the
pour. After pouring the alginate (see below) the foam block and
the dowel or screwdriver is removed prior to removing the gelled
alginate from the surrounding container.
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Photo #7
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7.)
Block the head into position by using a toothpick or straw section to
expand the mouth. (The use of a toothpick or plastic straw allows
for the brace to be snipped in two for easy removal after freezing the
head.) (Photo #7)
When the fish head is blocked to your satisfaction, place it on a
styrofoam plank and then freeze it, uncovered, until hard. When
frozen hard, retrieve the head and use snips or shears to cut the
toothpick braces from the mouth and remove them. LEAVE THE
STYROFOAM block between the operculae and the dowel handle or
screwdriver, as well. Place the fishhead into the molding form
(Pitcher, soda bottle, etc.) nose-down and suspend with a sturdy wire
inserted through a hole drilled into the dowel at the proper height, or
by bracing the screwdriver handle between two square sticks set at the
proper height. Make sure that a minimum of 3/4 inch is left
between the nose and the bottom of the container. Use a magic
marker to mark the dorsal (top) side of the head in position by making a
line on the outside of the container. (Illustration, Photo
#10)
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Photo #8
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8.)
Since the object of this exercise is to cast both the inside and the
outside of the fish head as an integral unit, the mold needs to be
formed in two parts. Alginate, by nature, does not stick to
itself, allowing for well fitting mold seams. That property will
be used to advantage in this technique. Most fish heads are shaped
as cones or truncated cones by design and form. The shape itself,
allows for easy removal of the head from the mold - EXCEPT that the
narrowing of the rear of the mouth at the gullet forms an hourglass
shape that prevents removal of the head following gelling of the mold
material. To preclude this, the mold is poured in two stages, the
first to shape the front of the head and the interior of the mouth, the
second to form the rear of the head from the gullet narrowing to the
tips of the operculae.
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Photo #9
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9.)
After positioning the fish head into the molding container, mix an
amount of alginate to cover the fish head to a point just beyond the
terminus of the upper mandible, or one half inch beyond the eye,
whichever is the greater depth. Mix the alginate well with the ice
water and pour around the suspended head. Allow the first pour to
set. Kill the setting time by cleaning out the container to ready
it for the second stage pour. Use a small scoop or blade to dish
out three small half-round keys into the gelled alginate surrounding the
head. (
Photo
#10
The shapes will enable you to re-fit the two halves together later.
When the keys have been cut, mix and pour the second alginate batch to a
point which just covers the styrofoam block between the operculae, or
the tips of the operculae if the block is long enough to extend beyond
the pour.
When
the second pour has gelled, cut a small notch into the edge of the
alginate to mark the point where the magic marker line is located on the
outside of the container. Remove the styrofoam block from between
the operculae and the dowel or screwdriver handle. The head will
remain in suspension at this point. Stick a filet knift blade or
other thin shim down the inside of the container to allow air to reach
to the bottom of the pour. If the container is a waste object,
such as a soda bottle, simply cut or drill a hole in the bottom for this
purpose. Invert the container and dump the alginate mass onto a
clean, wet surface. Gently pry the first half pour from the nose
of the fish, exposing the front half of the head. Using the scalpel,
make a cut, through the alginate only, from the center of the top
of the head to the top of the alginate mass. Gently open the
alginate like a purse and peel it away from the contained fish head.
You may make a few small relief cuts if need by, but it isn't necessary
to do that for most game fish species.
When
the fishhead is removed, fit the two halves of the alginate together,
using the keys to register them. When the seams are flush, and the
registration exact, replace the alginate into the container, aligning
the notch with the magic marker line. (The reason for doing this
is that some containers have fluted or specific bottoms or are irregular
enough to force this precision alignment.
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Photo #10
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10.)
When the alginate is in place, mix a quantity of fiberglass resin with an
amount of bondo, or other body filler. For most castings, a mix of
25% bondo to 75% resin is sufficient. Large fish, having thicker
heads may require a greater amount of filler. Normally, thicker
heads require less catalyst than do thinner heads, and the mix may
remain the same percentage for detail purposes, by reducing the amount
of catalyst used. Mix the resin and body filler well until
uniform and then add a sufficient amount of red crème hardener for body
fillers to cause the mixture to become a gray/pink color. too much
may cause cracking in large molds, too little will cause either a slow
cure, or failure to cure. There is no magic bullet for this part
of the process. When in doubt, mix a few small batches until you
feel the color and performance is controllable and proceed from there.
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When
the resin has cured, peel off the alginate and then use cold water and a
scrubbing with the tooth brush to remove all alginate from the casting.
(Any alginate missed will turn white after drying and can be easily seen
for removal purposes.) If all has been done well, the resulting
casting will be accurate and have all oral cavity and exterior details.
There will probably be some "flashing" around the head where
the two mold haves joined and the same on the inside of the mouth
cavity. Usually the flashing is very thin and requires a minimum
of effort for removal. (Photo
#8 and
Photo
#9")
Use a jeweler's or coping saw to cut the excess resin left between the
opercular flaps and to remove the sprue formed in the cavity left by the
dowel or the screwdriver. Small air holes may occur if you can't
vacuum the resin prior to pouring, or there may be small beads on the
surface left by resin filling air holes on the inside of the mold.
In either event, they are easy to remove or fill and cleanup of the
casting shouldn't take more than a few minutes.
NOTE:
The entire molding and casting procedure usually involves less than
thirty minutes of time when using Dental Alginate and around two hours
when using the Douglas and Sturgess product, due to the longer setting
time of the D & S alginate. That time allowance discounts the
freezing time for the positioned head, which may range from as few as
twenty minutes for a bluegill to a day or more for a tuna or marlin.
(Large fish head molds are made by a different process......This
procedure will work for most freshwater fish and many saltwater
species.)
TEETH:
Epo-Grip and others make some thixo compounds designed to build up teeth
to replace those missing in the casting. Large "canine"
teeth, such as those in muskie and barracuda and the like make be formed
from toothpicks or other shapes and then coated with epoxy. Shark
teeth may be made from shapes cut from briston paper and coated with epoxy. In any event, the small bumps in the jaws left by the
broken tooth bases will allow for correct and proper placement of the
ersatz teeth.
Good
luck and good casting!
Bill
Gaither (Cur) |
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Used with permission
from www.taxidermyreference.com
and Bill Gaither
Pictures and material copywrite by W. D. Gaither |
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