If you are carving an appliqué that you will likely use again, creating a mold and casting parts saves time and money. This article describes Dr. Francis Lestingi's three-part, step-by-step procedure ...
Casting an Identical Twin
I
didn’t see the value of the molding and casting process, until I visited Chicago
artist, Chris Maylone, at his studio on the city’s upscale far north side. Chris had taken an order to produce
twenty-five hand-carved Christmas trees for a retailer. Carving just one involved mind-numbing
tedious detail. Carving twenty-five of
the same thing would have been maddening.
Photo courtesy of Dr. Francis Lestingi, Signs of Gold.
By creating a mold of his carving, Chris could cast exact “spitting image”
copies of his original Christmas tree, finish the job on schedule and actually
make a respectable profit. More
importantly, the castings were harder and more durable than the original HDU
carving.
If
you are carving a part that you will likely use time and time again, such as an
appliqué for a sign, knowing how to create a mold and cast parts can be a
money-maker for you. In this article I
will describe a three-part procedure that I learned from Dr. Francis Lestingi,
former physics professor turned master sign carver and gilder. The three parts
of this procedure are:
1.
Creating the Model
2.
Making the Mold
3.
Casting the Duplicate
Creating the Model.
When carving the original model, make sure that the sides of the carving are perfectly perpendicular, with no undercuts. That way you can easily eject the parts from the mold. For carving the model, high density urethane (HDU) is commonly used, because it is very easy to carve. There is no reason to use wood, if all you intend to do with the original part is to use it to make a mold.
After
you have carved the model, lightly sand it.
Don’t overdo it or you will destroy the character of the carving. To prepare HDU models for casting, prime the
piece with two or three coats of Sign Prime, Jay Cooke’s All-Purpose Primer or
1 Shot’s Chromatic Hi-Build Primer. These
primers are designed to fill in the rough texture of the HDU, yielding a smooth
finish. Water based primers typically
dry in one to two hours, depending on the thickness of the coating and the
temperature and humidity in your shop.
High humidity above 80% can cause drying problems. After the final coat of primer is thoroughly
dry, lightly sand the surface with 320-grit sandpaper.
After
wiping the sanded surface with a tack rag, paint the model with a thick coat of
a Ronan bulletin color. Dr. Lestingi
thickens the paint by leaving the lid off the can to evaporate some of the
solvent in the paint. He prefers Ronan for this application to other paints,
because it is thicker, he gets better coverage and the final finish is
smoother. Once you have painted the model, it’s ready for the casting
process.
Making the Mold.
Making a mold is not difficult to learn, but it requires strict attention to detail. Here’s Dr. Lestingi’s step-by-step recipe for successfully making a mold.
Step 1. Whether you are creating a mold or
casting, you must work on a level surface.
“As my work surface, I use a piece of painted ¾” MDO,” says Dr. Francis
Lestingi. “On the bottom of the board I have attached four levelers which I
picked up at Home Depot.”
Step 2.
Next you must create a “confinement field barrier” or mold box to
contain the liquid rubber until it cures and solidifies. “You can use four
L-shaped wooden sections to create an adjustable mold box around your model,”
Dr. Lestingi says. You can build the L-shaped
pieces using two-by-fours or ¾” MDO plywood.
The advantage of using these L-shaped pieces for your mold box is that
it is reusable. It also adjusts to the
size of your model. (NOTE: To contain the liquid rubber poured around and over
your model you can also use other types of canisters, such as plastic food
containers, coffee cans or a plastic bucket. In selecting one of these
containers, just make sure that it is sufficiently large enough to provide ½”
clearance all the way around your model.)
Step 3.
Clamp the four L-shaped pieces together using clamps. Spring clamps are
fast and easy to use, but C-clamps will work, too.
Photo courtesy of Dr. Francis Lestingi, Signs of Gold.
Step 4. In positioning the model inside the
confinement field barrier, allow at least a ½” space around the entire piece.
Step 5. Secure the model to your work
surface. “There are a number of ways to secure the piece to your work surface,”
says Dr. Lestingi. “Screwing from the bottom certainly works, but it’s time
consuming. Some people also tack it place with hot melt glue. The problem with that is that the model is
raised slightly from the surface. What
works best for me is double sided carpet tape.”
Step 6.
Seal the edges of the confinement field barrier wherever the L-shaped
pieces join together and along the perimeter of the mold box between the pieces
and the work surface. Hot melt glue is
commonly used as a sealant.
“An
alternative is to use silicone to seals the edges,” Dr. Lestingi says. “The
problem with silicone is the potential of an adverse chemical reaction with the
mold compound.” Sealing the edges is
critical. Failure to create a good seal
will result in leakage of the silicone rubber mold material, which wastes
material, time and money.
Step 7.
Estimate the material required to make the mold. This is an important step. If you don’t mix
enough, you may need to start over from scratch, in which case all the time and
material invested up to then is lost.
Trying to compensate by mixing more than enough is not only unnecessary,
but it also wastes material and adds to the cost to produce the job. Mixing
just the right amount is the most sensible and cost-effective approach, and
it’s not that difficult if you follow the step-by-step instructions for the two
methods described below. “The second
approach involves a little high school math, which shouldn’t be too difficult
for most people,” says Dr. Lestingi.
“For those who are mathematically challenged, or if it’s been a while
since graduation day, just ask your granddaughter to help you with your calculations.”
The
simple way to determine the amount needed is to fill the confinement area with
water. Then pour it out into a measuring
beaker. Divide your measurement by two
because both Smooth-On OOMOO™ 25 and
OOMOO 30 are two-part silicone rubber compounds, which are combined in
equal amounts. Make sure to dry the confinement area completely or the water
will react with the mold ingredients causing bubbles.
The
faster, more trouble-free way to determine the amount needed is to do the math.
Here is the step-by-step explanation of the calculations that you will need to
make.
a.
Multiply length of the confinement area by the width and the height of the
model plus an additional ½”. This will give you the volume in cubic inches.
L
* W * H = cubic inches
Example: 9.25” x 10”x 1.5” = 137.75 inches³
b.
Next convert cubic inches to gallons.
Since one cubic inch equals 0.004329004 gallons, multiply that number by
the cubic inches calculated in the previous step.
Example: 137.75 inches³ * 0.004329004 gallons = 0.59632
gallons
c.
Finally, to convert gallons to fluid ounces, multiply gallons by 128, which is
the number of ounces in a gallon.
Example: 0.59632 gallons * 128 fluid oz. =
76.329 fluid oz.
A variety of mold resins are
available on the market. Smooth-On, for example, makes both a silicone and
polyurethane mold products. Each has its
advantages and disadvantages.
Polyurethane is very durable, but it requires the use of a mold release
agent when casting. Why is that bad? The
mold release agent can cause adhesion problems when either painting or gilding the cast part, if the part is not cleaned completely.
Although polyurethane molds will
outlast silicone rubber molds, for most applications the silicone rubber is the
most practical and preferred choice. Two
Smooth-On products that Dr. Lestingi recommends are OOMOO25 and OOMOO30.
Both products are two-part systems.
The OOMOO25 sets up faster in mold making than the OOMOO30. In approximately 75 minutes, the silicone
rubber is cured. After the components
are combined, the pot life of the OOMOO25 is fifteen minutes.
The OOMOO30 requires at least six
hours to cures. But the pot life is thirty minutes and the silicone rubber is
harder than OOMOO25 and more durable.
Before
mixing the components, thoroughly stir them with a paint mixing stick. In stirring, be sure to scrape the sides and
the bottom of the container, so everything is well mixed.
Because
the components are very viscous, it will be extremely difficult to pour the
liquids. Instead, carefully ladle the exact amount needed of each
ingredient.
Combine
the ingredients in a bucket. Dr.
Lestingi recommends using a popcorn-type of paper paint bucket, which you can
buy at your local hardware store.
Thoroughly mix the ingredients with a paint stick, making sure that you
scrape the sides and bottom of the bucket.
In
pouring the mixed ingredients into the mold, start at the lowest point in the
containment area. Continue to pour all of the material in that one spot. Do not
move around as you are pouring. By
pouring in one place, you will push all of the air out of the mold box. This
ensures that no air pockets will form. Also, do not pour the resin directly on
top of the model or you could trap air bubbles. After you have poured the molding compound,
Dr. Lestingi recommends that you wait overnight for the mold to thoroughly
cure.
Photo courtesy of Dr. Francis Lestingi, Signs of Gold.
The
next day, unclamp the L-shaped pieces and carefully pry the sections from the
formed mold and the work surface.
To
release the model from the mold, gently flex the edges of the rubber mold.
To
prevent dust from collecting inside the cavity of the mold, store it upside
down. Just before use, wipe the mold to
remove anything that doesn’t belong there.
Safety Note: Before working with any chemicals
“Read and Heed” the manufacturer’s safety precautions. Here are some general
rules that you should follow when working with these chemicals:
- Always
work in a well ventilated area.
- Always
wear safety glasses.
- Always
wear chemical resistant gloves and long sleeve shirts.
Cast the Duplicate.
For the casting process, Dr. Lestingi recommends using Smooth-Cast 300, a durable urethane casting plastic. Just as the molding materials come in a two-part formulation, the casting compound has a Part “A” and a Part “B”. These parts are mixed at a 1:1 ratio.
Caution: Part
“A” of the Smooth-Cast 300 contains
Methylene Diphenyl Isocyanate. Avoid contact with your eyes, skin or mucous
membranes. Do not breathe the fumes.
Over
the years, Dr. Lestingi has modified his procedures for mold making and
casting. One change that he has made is to add colorant to the casting compound
rather than paint the duplicate pieces.
He feels that this not only eliminates a step in production, which saves
time and money, it also produces a better finished product.
In
years past, he has experience some paint adhesion problems to the duplicate
piece. Although the number of failures
has been minimal, by eliminating the paint, he has eliminated any problems.
The
colorant that Dr. Lestingi uses is Smooth-On So-Strong Colors. Available in
eight tints (Black, Brown, Yellow, Purple, Green, Orange, Red and Blue) and two
opaque colors (white and fleshtone), the colorant is added directly to the “B” component.
To get the color you want, you will need
to experiment a little. As I usually recommend: “Test, Don’t Guess.” You can
add up to 3% of the colorant of the total volume. Don’t overdo it, or the silicone rubber may
not cure properly.
Step 1.
Determine the amount of casting material needed. For this step, use the easy water method,
which involves very little math. Just fill the cavity of the mold with water.
Then pour the water into a graduated beaker.
The amount of water is equal to the amount of casting material that you
will need. In the interest of keeping good records, mark the amount needed to
fill the cavity on the side of the mold with a permanent Sharpie pen. Before you start casting, the mold must be completely
dry. Any residual will moisture will
react with the resin causing it to foam. This will result in bubbles on the
surface of the casting.
Step 2.
Divide the amount of water measured by two, because you will need to mix
equal amounts of part A and part B of the two casting ingredients.
Set 3. Shake both jugs of the components to
ensure that all of the ingredients are well mixed.
Step 4.
Measure the amount of water which corresponds to the amount of one of
the ingredients needed.
Step 5. Pour the water into a clear plastic
cup and, using a fine tip Sharpie, mark a line at the height of the water
level. Do the same with another clear
plastic cup.
Step 6. After drying the cups, pour equal
amounts of part A in one cup and part B in another cup.
Step 7. Combine part A and part B in a third
cup. Quickly mix the two components for 45 seconds. Using either a chopstick or a craft (Popsicle)
stick, thoroughly mix the ingredients well, making sure that you scrape the
sides and bottom of the mixing container. When you work with the casting
product, you won’t have time to take a coffee break once you have started. The
pot life of the mixture is only two to three minutes. In that very short period time, you must mix
the ingredients and pour it into the mold. If you wait too long, the resin will set up in
the container before you pour it.
Photo courtesy of Dr. Francis Lestingi, Signs of Gold.
The
material is exothermic, so you should gradually feel some heat being
generated. The plastic resin will
continue to generate heat until the curing process is complete.
Caution: The
heat generated after combining Part A and Part B can exceed 212ºF (100ºC). At these high temperatures, you could burn
your skin. Be very careful when handling the mixed components. Even after the resin has cured, it will
continue to generate heat as the cast part cures.
Step 8. Pour the casting compound into the
mold.
Photo courtesy of Dr. Francis Lestingi, Signs of Gold.
Step 9. Wait 15 minutes for the casting
material to harden. If you feel the mold and it feels warm, the resin is still
curing. Wait until the piece is fully
cured.
Step 10. Carefully remove the duplicate piece
from the mold by gently pressing along the edges. The operative word is
“carefully”. If you are not careful, you
can very easy tear the plastic mold. To
help eject the piece, you can also press the bottom of the mold to force the
piece out.
NOTE:
If you are using a polyurethane mold, you must spray it with a
release agent prior to casting. Lightly
spray the entire cavity of the mold with the release agent. Then using a brush, coat all of the deep
recesses of the cavity with the release agent.
Finally, repeat the procedure.
Step 11.
Wash the duplicate piece with detergent and water to clean any
contaminant on the surface of the part.
If the molded piece has some rough spots, you can lightly sand these areas
smooth. Any surface imperfections or
surface textures will stick out if you gild the part, which detracts from the
finished appearance.
Step 12.
After you have finished casting, you will need to put your supplies
away. Once you have opened the two components of the casting resin, the
atmosphere will start to oxide the ingredients and they will start to
degrade. In one to two months the shelf
life has expired. You can extend the
shelf life of the product, by spraying XTEND-IT
Dry Gas Blanket (available from Smooth-On) into the container to prevent
oxidation. Immediately after spraying
the gas, replace the lid. The
manufacturer claims that XTEND-IT, will extend the shelf life up to four times
longer than normal.
Step 13 .
If you need to paint the cast part, Dr. Lestingi recommends Krylon
Fusion paint. This aerosol paint was
formulated specifically to bond to plastic surfaces, which makes it a great
choice for painting cast pieces.
Before
spray painting, don’t forget to prep the surface. Prepping plastic for painting
is a lot like prepping an automotive surface before applying vinyl
graphics.
“If
release agents or other contaminants are not thoroughly cleaned from the
surface of the plastic, you’re in for paint adhesion problems,” says Chicago
artist, Chris Maylone. “And once the
paint starts to peel, it doesn’t stop. You might as well start over.”
Maylone
recommends first washing the surface with hot water and detergent. This dissolves any water soluble contaminants
as well as any mold release agents, that may have been used. Cleaning with a solvent, such as a mild wax
and grease remover will clean any remaining contaminants. To play it safe, Maylone performs a final
cleaning with denatured alcohol to remove any oily film, that the solvent
leaves.
Unwanted
imperfections on the surface of the cast piece may require sanding. Wipe off any dust from sanding with a tack rag
and then wash the surface down again with IPA.
Sanding will scuff the surface of the plastic, giving it some tooth for
the paint to bite into. As an alternative, Maylone use a red Scotch-Brite pad.
“Roughing
up the surface with a Scotch-Brite pad doesn’t abrade any material from the
surface,” Maylone says. “It won’t
replace sanding. It merely puts fine
scratches in the surface of the plastic to improve paint adhesion.”
Priming the Plastic.
Following his surface preparation, Dr. Lestingi sprays two coats of Krylon. The first coat acts as a primer. The second is the finish coat. One advantage of the Krylon Fusion paint is that it dries fast. After an hour, the painted part should be dry enough to handle.
Krylon
Fusion comes in at least sixteen colors. Because Dr. Lestingi gilds most of his
cast appliques, he prefers painting the parts black. That way, if he has any holidays or voids in
his gild, he can spot them immediately.
Photo courtesy of Dr. Francis Lestingi, Signs of Gold.
Step 14. To attach the painted or gilded appliqué, Dr. Lestingi affixes
threaded studs to the cast parts. To
adhere the appliqués to the sign, he drills holes for the studs. After filling
the holes with silicone sealant and adhesive, he completes the installation.
Although
Dr. Lestingi has a master gilder’s Midas touch, he advises that you keep your
“cotton-picking”, greasy hands off of any gilded parts. As a general rule, he
does not clear coat his gold leaf work, because this would diminish the
brilliance of the gild. Touching non-clear coated gold leaf will transfer skin
oils from your hands to the gilded part, which could tarnish the gold. If you must handle a part, he recommends
wearing cotton gloves.
The Finishing Touch.
Gilding isn’t the only way to finish cast parts. Many of Chris Maylone’s project are painted. As an alternative to Krylon’s Fusion spray as a primer, Maylone uses a Kilz water-based primer, readily available at his local Home Depot for about $12 a gallon.
“For
priming, I use the Kilz product for just about all of my projects, including as
a primer for HDU,” he says. “It dries fast in about 30 minutes to an hour and I
can top coat it with either a water-based or oil-based paint.”
For
his finish coats, Maylone uses 1-Shot lettering enamels, artist’s acrylic
paints or Ronan’s Aquacote water-based bulletin enamels. “If I need a nice, glossy finish, I stick
with my 1-Shot paints,” says Maylone. “When it comes right down to it, I guess
I’m a 1-Shot guy at heart. Plus, it’s a reliable paint that I can count on.”
For
textures and special effects, Maylone uses artists’ acrylics. “With the
acrylics, I can easily create textures,” he says. “After painting a solid base
coat, I can apply three or four layer of glaze to create some subtle effects.”
When
using either the artist’s acrylic paint or Ronan Aquacote, Maylone uses a
variety of tools, including sponges and rags.
For brushes, he paints with
standard artist’s ox hair brushes and Langnickel Nocturna brushes.
For
Chris Maylone and Dr. Francis Lestingi, learning to make molds and to cast
duplicate parts, has saved them countless hours of valuable production time and
has improved their profit picture. “You can spend eight hours or more laboring over
a carving,” says Maylone. “And in 15 minutes you can cast a duplicate part.”
With that in mind, why wouldn’t take the time to learn these skills?
GILDING ARTICLES
NEW INSTRUCTIONAL VIDEOS. Five new videos have been added to RTape’s YouTube channel. The following is a description of the new videos:
Squeegee Technique. Nothing is more basic in vinyl application than the squeegee. But some squeegees work better than others. And there are right ways and wrong ways to use this simple tool. This video clip reviews squeegee selection, squeegee care and squeegee technique. Click here to view the Squeegee Technique video.
Wet Applications. Dry applications are typically recommended for most vinyl applications. For those exceptions to the rule, this instructional video explains the right way to perform a wet application. Click here to view the Wet Applications video.
Introducing AT65. Installing multiple color overlays with a paper application tape is not much easier than driving in the dark without your headlights. For these challenging applications, RTape developed its AT65, the universal high tack film. This video clip explains the features and benefits of this remarkable new film application tape. Click here to view the Introducing AT65 video.
Application of Window Graphics. Installing vinyl graphics on glass can be challenging, because the adhesive aggressively grabs onto this high energy surface. Repositioning graphics on window is generally difficult, if not impossible. This instructional video explains how to dry apply window graphics right the first time. It also describes the necessary steps required for surface preparation. Click here to view the Application of Window Graphics video.
Transferring Frosted Window Graphics Films. Because frosted window films are highly textured, transferring cut vinyl graphics can be problematic. This video provides direction in selection of the right application tape and how to apply these films quickly, easily and without problems. Click here to view the Transferring Frosted Window Graphics Films video.
Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer. Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.
Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for publications, such as Signs Canada, SignCraft, Signs of the Times, Screen Printing, Sign and Digital Graphics and Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.
© 2015 Jim Hingst
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