For anyone, who is carving an outdoor painted sign, your best raw material is usually High Density Urethane (HDU) sign board. Unlike wood, you do not need to be mindful of the grain direction when carving. For that reason, HDU is much easier to fabricate than wood. What’s more, because this synthetic closed cell foam material does not absorb water, it will not rot, decay, warp, or splinter.
If
you fabricate and install an HDU sign according to manufacturer’s instructions,
it should last between 10 and 30 years. One of the keys to creating a durable
sign is using adhesives, texturing materials, primers and paints which are
compatible with the signboard. That’s why I selected the Precision Board materials
by Coastal Enterprises. They have a complete system of products matched for
compatibility. What’s more, if you have questions, they have the service
organization that provides prompt, reliable answers.
Material Selection
High density urethane is available in a variety of densities. By varying the chemical formulation,
the manufacturer can control the degree to which the mixture foams and
consequently the density of the sheet. Density is the weight of the high density urethane per
cubic ft. The density ranges from 4 lbs to 45 lbs.
In
the sign industry the most common density is 15 lbs. However, for my project I
used the denser 18 lb. material. This heavier material is harder and stronger,
which allows you to carve more intricate detail. The 18 lb. material is also
smoother, so it takes fewer coats of primer to achieve a desirable finish. For
larger sign projects subjected to significant wind loads, many sign makers
select 30 lb. material. Just be aware
that the denser high density urethane costs significantly more. What can I say? You get what you
pay for.
One Part Urethane Glues
The
easiest way to either edge glue or face glue one sheet of HDU to another is to
use one part urethane glue, such as Precision Board PB Bond-240 HDU Adhesive.
This glue is similar to Gorilla Glue, but it foams less, which many sign makers
prefer, because it produces a tighter glue line.
What’s
nice about urethane adhesive is that there is no measuring. To activate urethane adhesive you just need to moisten the surface to be bonded by lightly spraying
the HDU with water, then clamp the pieces and you are done. More water is not better, so wipe off any
excess water with your hand.
To
build the thickness that I needed for the Tiki mask applique I glued four
sheets of high density urethane together. Prior to gluing the HDU pieces together, make sure that the
surfaces fit tightly so you do not have any gaps.
After
the surfaces are moistened, apply a thin coating of urethane adhesive using an
inexpensive squeegee. Kellie Miller of Precision Board recommends spreading the
adhesive to one surface using a tongue depressor. “As you spread the urethane adhesive,
pool the excess in the center of the board,” Miller says. “This technique
prevents air pockets from being trapped between the boards.”
After
the urethane adhesive is applied, position one board over another. “Apply weights to the
top of the boards so that the pressure is evenly distributed,” Miller
recommends. “Weigh alone won’t hold the boards in place. To keep them from
slipping and sliding out of place toe nail the board together in several places
with drywall screws.”
As the glued pieces are curing hold them in place with
drywall screws and weights.
Urethane
adhesives can expand near four times their original volume. In a couple of
minutes the adhesive will start to bubble. Join the surfaces together and clamp
the pieces using even pressure. Keep the
surfaces clamped for at least four hours. Full curing occurs after 12 hours.
You can expect some squeeze out. Remove the residual adhesive with either a
razor or a #3 carving gouge.
If
you have not worked with urethane adhesives, be advised that they are messy. For
this reason wear latex gloves and your grubbies. Also cover your work table
with application tape for easy clean up. Placing sheets of wax paper or clear
application tape underneath the glued pieces prevents gluing the high density urethane boards to your work surface.
Laminating with Epoxy
While
signs made from high density urethane have a number of advantages over redwood and cedar, one
disadvantage, is that it has neither the density nor structural strength of
wood. As a comparison, the density redwood is about 27 lb. per cubic foot,
which is nearly twice that of 15 lb. HDU.
Whereas
wood is comprised of long, sinewy fibers, HDU is made up of very tiny cells –
bubbles, if you will, that are formed in the chemical foaming process. These
little bubbles don’t provide a lot of structural strength.
If a
sign is subjected to significant wind load, you must support the HDU board in
some way to strengthen the panel. For the background of my Tiki Bar sign I used
a one and a half inch sheet of HDU, which I carved into as much as an inch deep
in some places. That didn’t leave me with much bulk the sheet. I felt that I needed extra strength so I
laminated a 2’ x 4’ sheet of aluminum composite panel (otherwise known as
Dibond) to a sheet of HDU of the same size. For this application the Dibond was
a better choice than wood or MDO, because it is not only lighter weight but
more importantly it is more dimensionally stable.
A
urethane adhesive would have worked, but epoxy glue provides better structural
strength and is great for bonding HDU to wood, plastic or metal. Unlike
urethane adhesive, epoxy glue is comprised of two components: the resin and the
hardener. These components must be mixed in precise proportions for the mixture
to solidify properly.
While
epoxy glue poses little potential for respiratory problems, you should work in a
clean, well-ventilated shop. It also
would not hurt you to wear an air respirator with a carbon filter for chemicals. Contact with your skin can
result in dermal reactions such as skin irritation, rashes and allergic
dermatitis. For this reason, always wear the chemical-resistant gloves,
clothing and other safety gear recommended by the manufacturer. If you are
sanding, wear a respirator with a particulate filter.
For
my project I selected a fast hardener. If you need additional working time, especially when working in warmer
environments, use a slow hardener. In combing the resin and hardener, you must
thoroughly mix the components for a minute or two. Be sure to scrape the sides
and bottom of the mixing cups so all ingredients are evenly combined. A mixing
stick with a squared end will get into the corners of the cup.
To
change the consistency of the resin/hardener mixture, you can add filler. It
can also be used as an extender. Selecting the right filler for your
application is the confusing part of using epoxies because there are so many
products from which to choose. I used a filler, which consists of microfibers
of chopped cotton. Using this filler creates a good multi-purpose adhesive.
The
microfibers not only thicken the epoxy glue, but they also give the mixture
tremendous strength. If the surfaces are uneven, the filler also produces a
mixture that will fill any gaps. When it
cures, it hardens like a rock, which can make sanding difficult. The different
fillers can be mixed together to produce your own special concoction.
In
thickening epoxy glue, add small amounts of the filler, little by little, until you
produce the desired consistency. For laminating flat panels of high density urethane and aluminum
composite panel, you will want the epoxy glue to have the consistency of ketchup.
When
bonding one surface to another with epoxy glue you need to follow a few guidelines:
• Make sure the surfaces are dry.
• In storage and during fabrication, the
surface of the HDU can accumulate dirt and dust. To clean the surface, slightly
abrade the surface with a grey Scotch-Brite pad. Before applying the epoxy adhesive, brush off
any residue from the surface using a chip brush and wipe it down with a clean
rag. Contaminants will compromise the adhesive bond.
• When bonding to a non-porous smooth
surface, such as the aluminum composite panel, rough it up with 80-grit sand
paper. This will give the surface some tooth so the adhesive bonds to it.
To
bond the high density urethane and the Dibond panel, used a two-step procedure. First, I coated
the high density urethane with epoxy glue without any filler using a foam roller. This ensures that
the epoxy adhesive wets out the entire surface of the HDU.
Right
after applying this first coating, pour the epoxy thickened with the filler onto
the HDU. If you are covering a fairly large surface pour the thickened epoxy glue in
the middle of the panel and spread it evenly using a notched spreader. You do
not need much epoxy adhesive to create a great bond. This type of spreader applies a
uniform thickness of epoxy glue and prevents air pockets from developing in your
lamination.
After
coating the adhesive to one panel, laminate the two panels together using
moderate pressure – just enough for the thickened adhesive to start squeeze
out. An alternative to using clamps to secure the panels as the epoxy cures is
to use drywall screws and weights evenly distributed over the panel. Too much clamping
pressure will squeeze out too much of the adhesive to from a good bond. It is
critical that you maintain pressure the two parts to be joined until the
epoxies cures, which is generally about eight hours. Failure to maintain
consistent pressure may result in the parts pulling apart, which will stress
the bond. Clean up any of the adhesive, as best you can, before it hardens.
Pot Life and Working Time
Pot
life and working times for epoxy can vary greatly based on the temperature of
your shop. The warmer the temperature is, the faster the epoxy cures. At 72°F
(22°C) pot life for a mixture can as little as 10 minutes. At 90°F (32°C) that
time is cut in half. That means that if you are working on a hot day, you
better work fast!
It
case you don’t know what pot life is, it is the amount of time that it takes
for resin and hardener to cure in your mixing cup before it hardens. Working
time, on the other hand, is the time it takes for resin to cure after it is
spread out onto the surfaces that you are trying to bond. Depending on the
ambient temperature, you can have as much as an hour for working.
Curing
to a hardened state can take as much as 6 to 8 hours. Complete curing takes
even longer. In about two weeks, the adhesive is nearly at full strength. (Don’t
be concerned if the adhesive on a test panel feels tacky before it cures
completely. The adhesive should harden as solid as a rock, if you follow the
manufacturer’s directions.)
So
why is there such a difference between pot life and working time? Mixing epoxy resin
and hardener creates a chemical reaction that creates heat. In a confined space
such as a mixing cup, you contain the heat. When you do that, the heat builds
up really fast. In fact, you can feel the heat as you are holding the mixing
cup. If you are mixing a big batch, the greater mass of material can generate a
lot of heat.
When
you pour the mixed epoxy glue onto your working surface, the heat dissipates. Using
the example of bonding Dibond aluminum composite material to the Precision
Board HDU, the metal surface can dissipate the heat fast. On the other hand,
the high density urethane does not dissipate the heat so fast.
So
what can you do? If it is impractical or impossible to control the temperature
of your work environment, the simplest solution is to use a slow hardener. If
you are mixing on a large surface, you can mix a smaller batch and spread it
onto the substrate. Then mix additional batches until the surface is completely
covered.
Carving HDU
In
cutting and shaping HDU, you can use many of the same types of power tools and
hand tools that you would use, when working with wood. To cut out the general
shapes of a design, the material fabricates easily using circular saws, band
saws, table saws, jig saws and routers.
Roughing Out the Design. After
gluing up the HDU boards for the Tiki Mask, I am ready to rough out the job. On
the ends of the boards I mark a semi-circular shape as a guide. Using a 4-1/2”
angle grinder with an 80-grit flap disk I rounded the edges of the HDU block.
An angle grinder can make short work of this stage of carving and is much
faster than using a gouge.
Using an angle grinder and other power tools makes short
work when roughing out a carving.
When
using an angle grinder, be sure to wear your safety equipment including a
tight-fitting respirator with a particulate filter and either a face shield or
safety glasses. You should also use ear plugs, especially during any prolonged
use of any power equipment.
Once
you have the basic forms cut, you can use standard wood carving tools, such as
chisels, gouges, knives, rasps and files. Because the HDU has no grain and no
knots, it will cut easier than real wood.
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| High density urethane carves easily using the same woodcarving tools that you use for carving wood. |
After
carving high density urethane with chisels, knives or rasps, you can use a variety of sandpaper
grits, ranging from a coarse to fine grit, to smooth any rough edges.
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| After roughing out the piece with an angle grinder, you can start detailing it using standard woodcarving gouges. |
Adding Texture to Your Carving
Precision Board has developed a couple of different coatings for creating textured surfaces. These coating are matched for compatibility for use with high density urethane boards. In addition to adding textures to your carvings, these coatings also strengthen the HDU.
The easiest coating to use is their TSF-45 Texture Surface Finish. There is no mixing. This water-based material comes pre-mixed in a can, ready-to-use. Not only can you use it on HDU, but it also works on other surfaces, such as glass, concrete and even metal. When the coating dries, it provides a tough, yet flexible surface.
Sign makers have used TSF-45 for all types of textures, such as wood and stucco. For my project, I used it to add a flowing texture to the torch flames. Uses are only limited by your imagination. Just make sure that you test any new applications, prior to production.
Before applying any coating to your carving, make sure that you clean off any surface debris with a chip brush or blow off any dust with your shop air hose.
Application of the TSF-45 is a two-step process. First you need to coat the surface with the pre-mixed texturing paste so that it completely wets out on the surface. This step is critical to prevent any delamination of the coating from the HDU.
To scrub the mixture into the surface, you can use different sizes of chip brushes which have been trimmed, leaving about ½” of the brush hairs. In a sense, this first application is a primer coat.
Then apply a second, smooth coating, which you can do before the first coating dries. If you follow the manufacturer’s instructions, the Precision Board coating will bond to the surface with no need for a primer.
Using a comb, notched trowel, sticks or even your fingers, you can create your desired textures. Before using TSF-45, the best practice is practice. In other words: “Test, Don’t Guess”. For my application I used a comb.
The applied coating is usually dried within 12 hours, but that drying time can vary depending on your shop temperature, humidity and the thickness of the coating. Be sure that the textured coating is completely dry before priming and painting. You can paint TSF-45 with a variety of water-based paints. “Because it is flexible, you should use a water-based primer and paint, which is also flexible,” says Kellie Miller. “Lettering enamels are stiffer than the TSF-45 and will not expand and contract at the same rate. What usually results is that the enamel cracks.”
Securing the Tiki Applique to the Backboard
One of the challenges in building the Tiki Bar sign was affixing the heavy applique to the backboard. To mount the Tiki I decided to use threaded rods epoxied into the body of the carving.
After the rods had hardened in the epoxy, I made a pattern for drilling into the backboard using brown kraft paper. You can make the pattern in a number of different ways. One of the easier ways is to paint the ends of the rods and transfer the impression of the rods onto the paper.
Using the paper pattern I drilled holes in the backboard. The next step is to make sure that everything fits together. Once that was done, I coated the backboard with thickened epoxy and secured the two parts together.
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| Chip brushes are helpful in scrubbing the primer and texturing material into the rough surface of the HDU. It helps to trim the hairs of the brushes to about 1/2", which stiffens the bristles. |
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| When painting a surface which has been textured with TSF-45 use water-based paints, such as Ronan's Aquacote or Createx Auto-Air paints. |
 |
The carving is secured to the back of
the sign using epoxy, screws and threaded rods.
|
To
ensure that no epoxy dries on the threading you can use a number of products.
Some people apply wax, cooking spray and even Teflon plumbing tape to keep the
threads clean and workable, so you can screw on your washers and nuts.
Doming the Letters with Epoxy
For
the copy on the sign I wanted a nice smooth finish. I had seen some signs where
epoxy had been used to create an ultra-smooth finish. In fact, it looked as if
the letters were domed.
Precision
Board makes a two-part modified clear epoxy resin that you can mix with paint
that will create this effect. The resin and the hardener mix at a one to one
ratio. “One of the great things about our PB Resin is that you can apply
directly to the HDU board,” Kellie Miller says. “There’s no priming, no
sanding, no painting.”
The
key to successful application of this material is measure exact amounts of the
resin and hardener and thoroughly mixing the components for two minutes. As you
are stirring, take care not to whip any air in the mixture. After mixing the resin, you usually have
about 20 to 30 minutes of working time.
In a
warmer shop environment you will have less working time. To extend the working
time, you can place the containers of resin and hardener in a refrigerator 15
minutes before use. After everything is mixed, you have plenty of working time.
At 75° F, you should have about thirty minutes.
After
mixing resin and hardener, you can color the mixture with lettering enamel.
Little by little add the paint, testing the mixture for opacity on printed
page. “You should use as much paint as it takes to block out the printing, but
no more,” advises Kellie Miller.
As a
general rule of thumb, you can mix up to a teaspoon to 8 oz. of epoxy
mixture. “For small batches, add the
paint a few drops at a time,” Miller recommends. Once the mixture is opaque
enough do not add any more lettering enamel. Too much paint can prevent the
resin from hardening.
 |
The PB Resin produces a smooth,
plastic-like, glossy surface for your letters. The background of the sign was
finished with Peacock Blue smalts supplied by Artisan Signs of St. Louis, MO.
On a
large area you can pour the resin directly from your mixing cup on the center
of the graphic. For smaller copy, you may want to use a squeeze bottle or
syringe to dispense the epoxy. After allowing the mixture to flow out, you can
coax the resin to the edge with a craft stick pulling not pushing the liquid.
To
ensure that the resin levels out evenly, make sure that you work on a level
surface. “If the surface is not level, you will break the surface tension of
the resin and it will spill over an edge,” instructs Kellie Miller.
Usually
a smooth, flat letter only requires one coat of epoxy. If you need to apply a
second coat, wait for the first coat to dry. Complete curing takes about 24
hours, after which you can paint or gild the surface. Clear resin must be
painted or it will yellow.
As
the epoxy is curing, air bubbles sometimes develop as a result of the chemical
reaction. Misting the applied resin with 91% isopropyl alcohol (IPA) will burst
the bubbles. If bubbles continue to appear continue to lightly spray the resin.
Priming and Painting HDU
Because
HDU is impervious to chemicals, you can use any type of paint to decorate it
including enamels, urethanes and lacquers. Before painting, however, the
surface must be primed.
Painting
without priming produces a very dull finish, which for most signage projects is
unacceptable. Many of the primers that sign makers use for HDU have very high
solids content, which coats the board with a thick layer of primer, smoothing
the rough texture of the HDU material.
Not
all primers are the same. A standard
primer only contains about 35% solids. The primer that I prefer is the
Precision Board brand by Coastal Enterprises, FSC-88 WB, which is comprised of
80% solids. What I like about this primer is that it fills in the rough HDU
texture in one coat, though I always apply two coats, smoothing the surface and
preparing it for the finish coatings. While you can brush FSC-88, you can also
coat the surface with a roller or you can thin it out and spray it.
Another
important feature of FSC-88 is it dries fast. In about 15 to 20 minutes it is
usually dry to the touch. Other primers can take forever to dry. That slows
down production.
|
 |
Precision
Board’s fast-drying FSC-88 primer is thick and smooths the rough texture of the HDU.
Before
priming high density urethane, you should sand the surface to remove and machining marks. After
sanding, clean any residual dust from the surface using a brush, compressed air
or a tack rag. Applying the primer paint with a chip brush usually works best,
because it is stiff enough to scrub the coating into the texture of the HDU.
When
you apply the primer, don’t lay it on too thick. A thick coat will take longer
to dry and can trap moisture that could lead to problems later. It is better to
apply two thinner coats of primer, rather than one thick coat.
Once
the primer is applied, direct a high volume fan over the coated surface to aid
the drying. “Drying under a shop fan is essential,” recommends Kellie Miller.
“The primer dries faster, and the flow of air prevents the coating from
absorbing ambient moisture. If the primer doesn’t dry properly, you run the
risk that it will delaminate from the HDU.”
|
To aid drying, position a high volume fan so it blows
over the primed surface, not directly on it.
After
the first coat is thoroughly dry, apply a second coat. Do not sand between
coats so you can build up sufficient mil thickness. After the second coat is
dry, then you can sand using 220-grit sandpaper. If the primer starts to ball
up as you are sanding, allow additional time for drying. After sanding, place
your sign under a shop fan again for an hour. This last step will prevent the
primer from reabsorbing moisture from the air.
Primed
surface can be painted with either enamel or latex paint. Be sure to dry sand
between each coat, using 220-grit wet & dry sandpaper. Sanding will smooth
the surface, removing any imperfections and will promote good inter-coat
adhesion.
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| After priming the surface, you can decorate your carving using either oil-based or water-based lettering enamels. |
Application of Smalts to the Background
For
the background of the sign, I ordered Peacock Blue smalts from Artisan Signs in
St. Louis. Artisan stocks 36 different
colors. Smalts, which is composed of either crushed glass enamel or colored
sand, was used by the old timers to decorate the background of signs many
decades ago. Glass smalts are usually
preferred because of its shiny, eye-catching appearance.
 |
Artisan Signs offers 36 different smalts
colors, each of which are matched to a color in the 1Shot lettering enamel
product line.
|
To
adhere the smalts to the sign substrate, many sign makers commonly use a 50:50
mixture of Smith’s Cream and Lettering enamel. The lettering enamel should
match the color of the smalts that you are applying. For convenience, Artisan
Signs provides chart on their website (http://www.artisan-signs.net/) matching
smalts with lettering enamels.
After
a thick, uniform coating of the adherent is applied the sign, the smalts is
sprinkled over the wet surface in a thick and uniform layer. Do not apply the
coating of adherent thicker than 1/8” or
it may not dry properly. One pound of smalts generally covers between 1.5 to 2 square
feet. My advice, however, is to order much more than you think you need. Apply
a generous coating of smalts. Any smalts,
which has not adhered to the sign, can be dumped off onto a drop cloth and
reused.
Repairs and Modifications
If
you make a mistake or want to modify your design, epoxy clay is a godsend. Like
other epoxies, it consists of two parts. One part is the resin. The other is
the hardener. When the two parts are mixed together, a chemical reaction
occurs. Working time is typically forty
minutes.
Heat
accelerates the curing process. So if
your shop is hot, the epoxy clay will cure much more quickly than in a cold
shop. Within two to three hours, the material is usually hard enough to be
carved, sanded and abraded with rasps and files.
To
mix an epoxy clay, such as Magic Sculpt, take two equal parts of the resin and
the hardener and roll each into two separate balls. Then "smush" or press the two balls
together, rolling the components to form a cylinder or rope shape. The color of
each component is noticeably different, which is a good characteristic. Continue
to fold and roll the epoxy clay until the two components are blended into one
uniform color.
To mix epoxy clay, roll two balls of hardener and resin of
equal size and smush them together until the clay is completely blended.
What’s
important is that the two parts are mixed well together. If the two parts are not blended
sufficiently, the epoxy clay will not cure properly and harden to its ultimate
strength.
After
mixing the epoxy clay, you can adhere it to your carving and mold it into
whatever shape you like. For my sign, I used it to form the head of the Tiki
torch. Wetting your fingers allows you
to smooth the surface of the clay. Hardened epoxy clay can be primed and painted with
the same paints that you use on your high density urethane carving.
To form the head of the Tiki torch, I used epoxy clay. TSF-45
Texture Surface Finish was applied to create the texture of the flames.
To decorate the textured flames I painted them using
Ronan’s Aquacote and Createx Auto Air paints.
Conclusion
Working
with HDU is relatively easy, but you need to follow a few simple rules to
ensure success.
- Thoroughly read the manufacturer’s instructions. Do not assume that the rules that apply to working with one product, such as an epoxy adhesive or primer from one manufacturer, are the same as those for a similar product.
- When working with new materials, always test the products before going into production. This ensures that all materials are matched for compatibility. As I like to tell people: Test, Don’t Guess.
- Before starting a job, assemble all of the tools and raw materials that you will need. This is especially important when working time is critical.
- Use the highest quality materials that your customer is willing to pay for. Remember: there are no shortcuts to quality and value.
RELATED ARTICLES
Using a Mini Angle Grinder for Woodcarving
Woodcarving Tool Care
Thinning Paste Wax for Easier Application
Applying a Wiping Varnish to Your Carving
Using Epoxy Clay to Correct Woodcarving Mistakes
Safety Rules for Angle Grinders
Lowering the Cutting Angle of Woodcarving Gouges
Undercutting to Create Drama in Relief Carving
Woodcarving Tool Care
Thinning Paste Wax for Easier Application
Applying a Wiping Varnish to Your Carving
Using Epoxy Clay to Correct Woodcarving Mistakes
Safety Rules for Angle Grinders
Lowering the Cutting Angle of Woodcarving Gouges
Undercutting to Create Drama in Relief Carving
About Jim Hingst: Sign business authority on vehicle wraps, vinyl graphics, screen printing, marketing, sales, gold leaf, woodcarving and painting.
After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.
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 500 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published. Vinyl Sign Techniques is available at sign supply distributors and at Amazon.
© Jim Hingst 2018
Stunning work. Thanks for sharing.
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