Kobracast Art

We teamed up with Gillian of All Tomorrow’s Patterns (GillianConahan on IG) for a tutorial on building a sword with her preferred stabilizer – cardboard or cardstock instead of foam! This allows a lighter, sharper finish, which can be excellent for bladed weapons and large builds! 

Materials:

– Thin cardboard or book board (about 1.2mm thickness, solid all the way through and smooth on both sides)
– carbon kite rod or other thin, rigid support core
– Worbla’s Kobracast Art for internal support on the blade
– Worbla’s Black Art for the hilt and detailing
– twine to wrap the hilt for bulk
– light-bodied acrylic gesso or your preferred primer
– light-bodied acrylic paints in your preferred metallic shades plus black
– glass cabochons for gems
– leather scrap and heavy linen thread for hilt wrap, plus a scrap of felt for padding.

I like to use cardboard as a base for sword props, especially the blade portion, because it’s lightweight, can be cut with just a craft knife, and it creates flat, smooth surfaces and edges with relatively little effort. You can also crease it to create added structure and rigidity, which I used to my advantage for this large unusually-shaped blade. The cardboard is solid all the way through, smooth and uncoated on both sides and about 1.2–1.5mm thick. I got a large sheet from an art store, but also stole the cardboard off the backs of several notebooks to cut smaller pieces. (I’ve used thinner oak tag for other projects, but found that it wasn’t rigid enough for this wide blade and tended to curl and lose its shape.)

For this build, which is based on the Dawn Court Warlord’s battle gear from volume 5 of Monstress, I started by drawing the pattern out by hand on tracing paper. I find it easiest to work full size for large props, as it gives a more intuitive sense of the proportions.

Blade

Transfer the blade design to the cardboard by rubbing a soft pencil on the back of the pattern and using a hard pencil or ball-point stylus to go over the outline from the front. Draw in the crease lines down the center of the blade and around each of the curved edge bevels, then score them with an awl so they bend cleanly. This gives the blade almost enough dimension to hold its shape even before adding the support.

Next, rough cut Worbla’s Kobracast Art to fit each half of the blade. Kobracast has a pronounced texture that can require a lot of finishing if you use it on a surface face, so I like to use it on the inside of the cardboard and use the smoother, sandable paper as the outside. Kobracast is very lightweight and can warp and flutter unpredictably as it heats, so it helps to leave a little extra and trim it off later. It’s also important to heat it evenly all the way across the piece so that the stiff cold areas don’t pull the softened areas out of shape. Weight one end to prevent it from shifting and start heating from the other end, sweeping slowly back and forth across the blade while moving along its length.  The material is very sticky and just needs to be pressed down lightly to adhere it to the cardboard. Once the piece is smoothly covered, trim away the excess and make sure all areas are firmly adhered, reheating and pressing down as necessary. 

The large projection on one side of this blade turned out to need a little extra support, so I cut an additional piece of cardboard that I just stuck to the inside of the Kobracast, making sure to keep it a little way from the edges so there’d still be enough adhesive to hold the two halves of the sword together. This is also a good time to insert the core support for the sword, in this case a 12mm pultruded carbon tube that I ordered from a kite shop and cut to length with a hand saw. Kobracast is very sticky when activated, so usually nothing special is needed to keep the support rod in place. If you have a thin rod or thicker blade and need to pad the support to keep it centered, you can roll up your Kobracast trimmings into sticky ‘snakes’ that will cradle the rod and hold it in place. 

Next, heat both halves of the blade evenly around the edges and carefully match them up, adjusting the creases so they meet perfectly around the edges. If there are points where the curves are a little sharper and the edges don’t want to stay together, you can roll up more Kobracast scraps and insert them between the layers like an adhesive putty.  After everything is well adhered and cool, use a craft knife to smooth the edges and bevel away a little of the cardboard thickness so the edge is thinner and more bladelike – though obviously for safety reasons you don’t want to go TOO sharp. Fine-grit sandpaper also works well for smoothing and getting rid of paper fuzzies. 

I cut out and scored the wedge-shaped detail for the base of the blade in the same way, but beveled the underside of the cardboard before adding the Kobracast to make the join a little smoother. To attach pieces like this, simply heat the edges to activate the adhesive and press in place. (9) Low-relief details like the flame shape on this blade can be cut from cardstock and adhered with a glue stick, but you may wish to test your paper with the primer you’ll be using later as some types will warp and ripple when moistened.

Hilt and Pommel

Next is building up the hilt of the sword, as it’s easier to wrap and smooth before the cross guard is in place. Start by roughly sculpting a stopper on the end of the support rod, using a scrap of Kobracast for the stickiness covered with Worbla’s Black Art for the main shape. To get an easy disc shape, cut a narrow strip of Black Art and wind it around the support rod in a spiral to the desired radius. 

Kite rods are too thin to make a comfortable hilt, so bulk it up with twine to achieve your desired thickness. First, wrap a scrap of Kobracast around the support rod, which helps to secure the twine and prevent it from rotating around the rod. For a more oval-shaped hilt, first cut scraps into strips and lay them along each side to create a wider, flatter profile. (This is a great place to use up your very ugliest scraps – these were from a failed experiment and still have paper shreds stuck in them.) 

Secure the end of the twine and start wrapping, heating as you go so that the first layer is solidly adhered to the hilt, although I try not to heat the bare support rod too long or too directly to avoid any chance of warping it or potentially releasing harmful fumes (depending on the composition of the support material.)  Continue wrapping the twine until the hilt is nearly large enough, then tie off the end and made sure it’s well stuck in the Kobracast.  Measure the circumference and cut a strip of Black Art just large enough to cover it. Some bumpiness is likely depending on the smoothness of your twine wrap, and you can either leave it for an interesting grippy texture or go back in and smooth it by hand with sculpting tools. I planned to finish my hilt with a leather wrap, so I just did a cursory smoothing pass.

Sculpt the pommel by shaping Worbla’s Black Art around the stopper you already built. There’s no real trick to this – I started by rough cutting a stack of scraps for each side of the pommel and squishing them together around the end of the support rod, then progressively smoothed and sharpened the details on one side at a time.  I do almost everything with one basic wooden sculpting tool, which I’ve rubbed with olive oil to prevent it from sticking to the Worbla. To avoid inadvertently squishing parts you’re not actively working on, try to heat only a small area at a time and allow it to cool and firm up before moving on to another area.

When working with a solid mass of Worbla like this, I try to time the heating/cooling cycle depending on what kind of sculpting I need to do. Blending edges and smoothing wrinkles is best done right after heating, when the outermost layer of Worbla is as hot and soft as it’s going to get but the interior is still firm. As the heat distributes through the whole thickness of material, large-scale reshaping becomes possible. Finally, sharp edges and fine details are easiest to achieve as the surface cools and begins to firm up again, when it’s just on the edge of being too hard to work with.

Crossguard

Once the hilt is wrapped, you can start building the crossguard on top of it. For complex designs, you may need to build this up in layers, looking at which components are thicker or overlap other components. In this case, I identified three distinct segments: the cat’s eye shape that holds an inset gem, lower prongs, and upper prongs. Each would be patterned individually and then assembled around the hilt.

I’ve gotten great results from a ‘sandwich’ method using Kobracast on the inside and Black Art on the outside, as the extremely sticky Kobracast is helpful for joining pieces and the Black Art is great for sculpting surface detail. 

Joining up the crossguard can get a little tricky because it needs to wrap around the widest part of the blade and hilt but still meet at the edges of the prongs. Unless you’re an outstanding patternmaker or do a ton of trial and error, you’re likely to have some gaps where the pieces are supposed to meet at the edges. You can compensate for this by adding a rolled-up Kobracast scrap to each side to increase the contact area when the pieces were squished together, then sculpting Black Art scraps across the edges to smooth and refine them.  If you need more material to work with in any particular spot, like I did when sculpting the bevels, you can lay down scraps wherever they’re needed and blend them into the surface with a sculpting tool. 

Gems and Detail Sculpting

My favorite way to do custom gems is with clear glass cabochons, which can be ordered inexpensively in lots of different sizes and shapes. Paint the back of the stone with metallic paints, using a soft brush and several thin coats to get smooth coverage, or place metallic paper in the Worbla setting behind the stone, and the result is a very clear, shiny stone with a surprising amount of depth.  You can also basically ignore them when painting the prop, as any stray smudges of acrylic can be scratched off the glass without damage using your fingernails or a wood or plastic tool.

To create the relief design, roll small pieces of Black Art into snakes and shape them into tapered bevels by hand. For repeated elements like the symmetrical designs in front and back, make sure they’re all the same size by cutting half-inch strips of material from your scraps and measuring off the same length for each element of a set. Keep a copy of the detailing pattern handy so you can check the shapes as you go. 

To set the gem in, first level the area by cutting away overlays and building up layers of Black Art around it as needed. Place your prepared stone and lay doubled strips of Black Art over the edges to hold it in place, then use sculpting tools to shape them into your desired bezel shape. The glass stone retains heat, so it helps the surrounding area to stay soft longer and makes it very easy to sculpt. Once the gem is secured, heat both the surface of the hilt and your additional embellishment pieces and gently press them in place. Finally, go back over the details with a tool to sharpen them up.  Make sure the piece is fully cool and hardened before flipping it over to repeat for the other side of the hilt.

Here you can see the finished sword base, ready to prime and paint.

Primer and painting

As soon as the blade is done, even before you finish sculpting the hilt and crossguard, you can start applying coats of primer to help seal and protect the paper surface. I like using acrylic gesso for the exposed cardboard blade, because it’s relatively dry for a brush-on water-based sealer and it dries to a semi-flexible sandable finish. Although the gesso needs multiple coats with up to a day to cure before sanding, this is an easy step to do on a weeknight when you might not have the time or energy for sculpting. If you’re impatient like I am, you may want to also work on other parts of the costume so you’re not tempted to rush the dry time. Black Art tends to acquire a very smooth, hard surface after sculpting, so you may need to sand it lightly to help the primer adhere. Apply several thin coats, being careful to avoid drips as they can cause the primer to chip or peel when sanded. 

Make sure to use breathing protection when sanding. I use a fine grit sandpaper and sand until the surface has a smooth, papery texture, as more than that is probably overkill for brush painting. If airbrushing or using another spray finish you may wish to go smoother. The water-based primer does not respond especially well to wet sanding, but you can use a slightly damp cloth to wipe away any dust once you’re finished.
Follow with a base coat of acrylic – black works well for most metallics, or you can try red for warm golds. I paint with light-bodied flexible acrylics to minimize brush strokes and cracking.  I often find gold and bronze metallic acrylics to be too warm-toned for my taste, but I’ve noticed that metallics tend to get muddier and less saturated when mixed so I dull the too-brassy golds down by mixing with silver or black metallics.
In addition to the main colors for the hilt and blade, select or mix at least one highlight and shadow color for each. Put down your base layer of mid-tone metallic, then look at where the shadows and highlights fall naturally on the surface and follow those lines to exaggerate the effect. For example, the weight balance of this blade means that it naturally orients itself in a particular direction when held, so the same side always faces down. This allowed me to paint the lower face of the blade a darker color to emphasize the shadow, and be confident that it will look natural in most lighting. Finish off by dry-brushing black into the corners and crevices, where grime and patina would naturally accumulate and not be removed by polishing. You can also add more highlights to corners and edges that would be likely to be rubbed smooth by wear. 

Leather Wrap

To finish off the hilt, you can sculpt and paint like the rest of the sword, wrap the handle with strips of fabric or decoratively patterned cord, or make a stitched wrap with leather or fabric. For a leather wrap, cut a piece of leather to fit around the hilt, with enough extra around the edges to tuck them to the inside for a neat finish. Fold in the edges and hand or machine stitch, then glue a piece of felt to the inside to smooth and pad the grip.  Spread glue on the inside of the wrap to hold it in place while you stitch it closed, then stitch the two sides together around the hilt, positioning the seam on the downward side of the handle to keep it unobtrusive.  You can also embellish the wrap however you like before stitching – details like cording, studs, or embroidery are all great options for adding texture and grip.

There you have it! A lightweight sword with a core of cardboard, some Kobracast Art, and details made from Worbla’s Black Art.

Thanks again to Gillian, Gillian Conahan on IG,  All Tomorrow’s Patterns, for partnering with us on this build!