Custom Glass Castings from Digital Designs

This post is a follow up to a previous one about techniques that I have been exploring to transfer digital designs into cast glass objects. This began last year at a fellowship at  Wheaton Arts’ Creative Glass Center of America and was expanded upon this year while teaching at Pilchuck Glass School and in a workshop at Detroit’s College of Creative Studies. In particular, I have  focused on one particular technique; using a low cost desktop CNC machine to carve reusable graphite molds for glass casting multiples. There’s a few design limitations to this approach, but it is an amazingly cost effective approach to creating small to medium scale runs of custom designed glass tiles. The molds hold up for hundreds of castings, and possibly even more, so this is an exciting way of creating custom glass design objects and custom tiles for architectural applications. This will be a big focus for much of my work in 2017.

With a clean and simple design, these new geometric tiles channel the 1980’s era video game Qbert, Islamic mosaics, and leverage the material’s clarity and sparkle. I love the simplicity and the illusory way we see through the smooth top surface to see the relief texture on the backside. I am thinking this will become a set of tabletop design objects, with 6″,9″ and 11″ sizes that interlock. However, I am almost more excited to think of them as architectural tile. How cool would it be to have a wall made of these, or have them as accents embedded in concrete?

Below you will see some of this new carved graphite mold work, as well as some student work from teaching at Pilchuck this summer.  Design constraints of this method center around the fact that this process does not support forms with undercuts. Likewise, the machine can only mill material up to ~2.5″ thick and can only do straight plunge cuts as long as the longest router bit you can find. For most 1/8″ bits this means you cannot do any straight cuts more than 1.5″ deep. However, because graphite is a lubricant and it pretty impervious to heat, once the moisture leaves the material after the first few casts, these molds can be used over and over again, with beautiful results. For any schools or glass studios who are looking to create such a setup, I have created a bill of materials for creating such a setup, totalling under $2500. (BTW, I am available to teach workshops! )

The top of the casting is flat, perfectly magnifying the relief texture of the underside.

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CNC milling the graphite mold

Completed rough pass on CNC, ready for finishing pass

Ladling molten glass into the finished mold

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The tile on the left is upside down, showing the relief on the backside. The relief side is as nice as the front and they would make a beautiful glass brick wall.

I’ll end with some images from the TaDDDaa!!! class at The Pilchuck Glass School this summer. It was a three week deep dive into 3D modeling, scanning, printing and CNC carving. Here’s some of the class’ work with graphite for glassmaking:

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This was my first test with this technique at Wheaton Arts and the process used by students for the class at Pilchuck. Here we see rough and smooth CNC carving of the graphite mold, hot glass in the mold, and final product at room temperature.

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The TaDDDaa!!! class at Pilchuck was a three week deep dive into 3D modeling, scanning, printing and CNC carving.

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My TA Christian with Phirak and Rebecca, who will be teaching a 3D printing clay class at Pilchuck next summer

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Rebecca’s mold based on a victorian pattern

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Jameszie made a Ouija planchette

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Brent supervising his first carve

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John, Lee, Phirak and Nikki trying out their molds

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My student John was a master mold maker so he undertook making a two part blow mold and spent quite some time finishing the graphite to a polish

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Blowing glass into the mold

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Michael’s two part blow mold

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A pile of hot casting molds cooling down at the end of the class casting session

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A fishscale tile design I was playing with

CNC Carving Glitch Art

Greetings from the woods of Stanwood Washington where I am teaching in the remote paradise known as the Pilchuck Glass School. Session 2’s theme is Play and our class has been playing with methods of creating glass castings from digitally generated sculptures. 

As part of the class we are CNC carving graphite molds so I brought a bunch of graphite that I bought on eBay. I had previously carved blocks that I had bought from this guy with no problems so I was bamboozled when I started to have carving issues with my molds here. I spent the better part of the last two days wrestling with the XCarve, thinking the axis slipping was mechanical. Then I realized the carbide bit was totally shot and realized the problem. The CNC is finally back to carving the other/ softer graphite like it was butter. I finally carved this mold I’ve been trying to make, but only did the rough pass. I think I like the terraced stepping… What do you think!? 

In the meantime, please enjoy my latest work with graphite glitches….







Explorations of Processes for Digitally Created Glass Castings

I spent much of 2015 taking a year long flexible fellowship at Wheaton Arts’ Creative Glass Center of America developing ways to cast glass from computer generated sculptural forms and wanted to take some time to share these learnings. I worked extensively with glass many years ago but now create most of my art with 3D scanning and printing. The Wheaton Arts’ fellowship was a unique opportunity to bring these two practices back together.

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Wheaton Arts is home to the Creative Glass Center of America in Millville, NJ, where I had a fellowship this past year to conduct experiments and create a workflow for casting glass from computer designed objects.

My work in the last few years has used a combination of 3D modeling techniques. I usually begin with 3D scanning,  primarily structured light scanning with Primesense/Kinect style devices and occasionally photogrammetry for non human subjects. Other non-organic forms are just modeled directly in the computer using my software of choice Zbrush. Next I will digitally manipulate and sculpt the 3D scans in the computer. Finally the work is output as a 3D print. My investigations this year took these techniques further, so that these digital sculpts were then realized as cast glass forms. I tried a few variations of lost PLA casting, as well as CNC milling graphite to make reusable molds. Enjoy.

Lost PLA Kiln Casting

The first technique I chose to explore is what people are calling “Lost PLA”, basically an evolution of the traditional lost wax kiln casting technique. Starting with a 3D printed positive of the form I want to cast in glass, I created a plaster/silica mold around my 3D print.

The actual recipe for the mold by weight was:

  • 16  parts water
  • 6 parts Hydroperm
  • 6 parts Plaster
  • 6 parts Silica (or olivine sand)
  • 1  cup 3/4″ fiberglass strand

This could be done with just a 50/50% plaster-silica mix, but as I understand it the Hydroperm foams and creates air pockets in the molds to make them lighter. The fiberglass strand helps strengthen the mold and helps wick out the moisture so the molds dry more efficiently.

I began by plugging any holes in the surface of the 3D prints with microcrystalline wax and waxing the prints down to a table. I then just cut strips of tar paper and hot glued them down to form a wall around the print, leaving room for about 3″ of mold thickness. I mixed a small initial coat of mix with no fiberglass strand to use as a splash coat over the object, then mixed subsequent buckets of mix to fill the molds completely. After the mold was filled, I let it set before tipping the molds on their sides to dry (having fans helped this).

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3D Print affixed to the table with wax and surrounded by a cylinder of tar paper

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3D prints and tar paper prepped for casting molds

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Splash coat on the 3D print

 

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Mold ingredients being dry mixed before the water is added

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Completed molds drying

After a minimum of one day drying (and preferably more like a week), the molds were ready to be loaded into the ovens. The PLA was still on the inside and needed to be melted out. With lost wax casting, the general practice is to steam the wax out of a mold. I tried this with the 3D printed PLA and barely got it to move at all. Steaming out PLA is not an option so it has to be burned out in an oven.

Even though PLA is a biodegradable corn starch, the burnout is smoky and not good to be around so it had to be timed to happen overnight when the studio was empty. I would begin by soaking the oven at 300˚ for about three hours and then pushing it upwards at about 100˚/hour. At about 450˚ I would go in (wearing gloves, glasses and a respirator) and use pliers to pull out some big chunks of plastic as it started melting. I had to be careful not to damage the mold in doing so. At about 700˚, I would go in with a stainless steel turkey baster and suck out as much molten plastic as possible. The oven would then go to 1000˚ for an hour and be fully burned out. Because burn out in an oven is pretty nasty smelling at its peak and I can’t really recommend it as a best practice. However, I just became aware of Moldlay– a 3D printing filament designed for lost wax casting. It’s expensive but I would like to check it out.

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Mold mid burnout

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Molds at 1000˚F after burnout

From there I tried two basic approaches to casting into the plaster molds. The first technique involved putting molten glass from a furnace directly into the molds. The second involved cooling the molds back down, packing them with chunks of crystal glass, then firing them to melting point. Each techniques has its strengths and weaknesses.

Lost PLA Kiln Casting Technique 1- “Hot Glass Lacrosse Casting”

Since buying crystal to kiln cast with is very expensive, I was trying to be more cost effective by using the readily available furnace glass to cast with. Basically, after the mold was burned out I would soak it at 1000˚ for several hours to burn out any chemical water, and then we would ladle glass directly into the molds. I found that even after I soaked the molds 10-12 hours at 1000˚, the chemical water in the plaster would still cause the glass to bubble up as we poured the glass in. We then resorted to a technique we called Lacrosse Casting. I would gather a ladle of glass, then dump the ladle into a second ladle someone else was holding. They would rock the ladle side to side so that the molten glass skinned up on the outside a little. They would then dump that back into my ladle and I would go to the oven and gingerly drop this “hot tamale” of glass into the mold. The center of the glass was still quite hot but the skinned up exterior was less likely to bubble. Unfortunately the molds are quite fragile and this can cause damage if there are a lot of delicate details to the mold. After the mold was filled, the oven would be sent up to about 1500-1600˚ to make the flatten out and flow into the mold. As soon as the glass flattened, the oven was crashed back down to under 1000˚ and an annealing cycle began.

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Passing off ladles full of molten glass in order to cool the exterior of the glass before dropping it in the fragile molds

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The 2300˚ “lacrosse” pass

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Dropping glass into the mold

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Crashing the oven after it reaches 1600˚F and the glass has flattened out

Issues with this technique

  • This process takes a lot of time! I was casting forms that took 2+ days to print, then there was mold making, casting and annealing.
  • The plaster molds are extremely fragile and can easily be damaged by the glass as it is dropped in the mold. This results with imperfect castings that often have bits of plaster encased in the glass.
  • If the ladles are not very clean, the glass will often have veiling from the ladle surface. Bubbles are also often introduced resulting in a very bubbly glass. In my case I liked the underwater look this gave.
  • Devitrification is a crystalizing of glass that happens at approximately 1200 degrees, making the surface of the glass fog up. Soda lime glass (Spruce Pine batch) is particularly vulnerable to this. In my case, if there was not enough radiant heat above the top of the mold and it took too long for the oven to heat up for the glass to level out in the mold, the surface would fog up.

Sample Castings (Unfinished work)

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Death (work in progress) 14″x 14″x 6″

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Creation (work in progress) 14″ x 14″ x 5″

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Untitled work in progress 14″ x 14″ x 4″

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The Gates of Heaven 24″x 19″x 5″

 

Lost PLA Kiln Casting Technique 2- Kiln Casting

The issues with molds being damaged by hot glass and devitrification lead me to acquire some crystal to kiln cast with. Casting crystal is expensive and usually formulated to not devitrify so in general this technique delivers more optically pure castings. I tried two glass formulas for kiln casting; Uroboros Glass’ system 96  and Schott optical crystal.

After the mold is burned out, I would let the oven slowly return to room temperature so I could carefully vacuum it out and pack it with chunks of glass (My glass came in large tiles so I cleaned the surface with alcohol and then used a torch to shatter them.

Bang! #glass @wheatonarts

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The small chunks could then be loaded in the mold, and the oven slowly brought back up to about 1550˚ until they melted in completely and the worst of the bubbles came to the surface. At that point the oven was crashed back down to under 1000˚ and the glass is annealed (slowly brought to room temperature).

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Loading chunks of crystal into the mold

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Close up of mold and crystal chunks. I like how the mold picked up the layer lines from the 3D print.

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The oven is ready to be heated back up

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At about 1550-1600˚F, the glass is molten and flowing into the mold

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Its a delicate balance how long to keep the mold hot. You want to get the bubbles to rise to the surface, but also want to stop before the glass begins to devitrify and fog on the surface.

  • This technique definitely yielded the best casting results for Lost PLA
  • More expensive- both in the time consuming process, oven time and  most significantly the cost of the casting crystal
  • Devitrification can still be an issue, depending upon the glass used
  • The final casting still requires extensive grinding, polishing and finishing work
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Angel/Mermaid (work in progress) 14″ x 14″ x 6″

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Funny Face (work in progress) 14″ x 14″x 6″

Hot Glass Casting into CNC milled graphite molds

I quickly realized that the lost PLA technique was time consuming and disconnected from all the excitement and spontaneity that I associate with hot glass work. Lost PLA castings also required extensive work divesting from the mold, then grinding and polishing. I had long wanted to experiment with CNC carving as opposed to 3D printing, and set out to experiment with milling graphite to create reusable molds as a more cost effective approach for casting glass with.

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CNC milled graphite molds for glass casting; rough pass carving with 1/4″ endmill, finished mold cut with 1/8″ ball mill, molten glass in the mold and annealed, cooled glass casting

I decided to purchase the Inventables XCarve  because it is an open source CNC machine, and I wanted to support Inventables great work in making CNC software more user friendly. I opted for the 1000mm version with the heavy duty Nema 23  motors and Dewalt 611 spindle which has enough power to even mill aluminum. I had a lot of trepidation about building a kit as some of the 3D printer kits I had built in the past were not well documented, but Inventables documentation was excellent and it worked pretty well right off the bat. A few support calls and posts on the message boards got me through the few small hiccoughs that I did encounter.

However, I was concerned about milling graphite as the dust is electrically conductive. If that dust got all over as I was using the machine, not only would it make a mess, it could also fry the Xcarve Arduino controller, and even the laptop driving the setup. I had no choice but to rig up a robust dust collection system. I ended up buying a dust shoe from KentCNC to mount around the spindle (Yes, I could have made my own but was running out of time at Wheaton by then). This then attached to a Dust Deputy cyclonic dust collector and a shop vacuum. The result was a powerful dust collection system that captures nearly all the graphite coming off the spindle as it cuts, and 95% of it ends up in my new favorite tool, the Dust Deputy.

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The newly assembled X-Carve, still in need of some wire management

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Unlike 3D printing, CNC milling has the machine doing multiple passes. Shown here is the rough pass, done with a 1/4″ endmill.

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The finished mold, cut with a 1/8″ ball mill

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The big test… Trying out the mold for the first time!

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Torching the glass as it sets up in the mold

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It looks amazing!

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The final result- a cast glass tile from a mold that will stand up to hundreds of castings!

Coming out of the last year of experiments, I’m most excited about this process as it has a lot of potential for small run computer designed glass objects and custom tiles for architectural use. There are some design restrictions in that molds cannot have undercuts and the Xcarve can only cut about 2 1/2″ at the deepest, but because these molds can be quickly and comparatively cheaply generated and used to create cost effective editions, I think this approach has a lot of promise. I look forward to continuing to experiment with these techniques as I share them with my class this June at the Pilchuck Glass School.