Kiln Casting for a Pendant using the Lost Wax Technique

​The Grass Orchid in Glass

Shortly before Christmas last year I got a request for a “masterpiece” pendant. It was to depict the Grass Orchid – a theme representing Spring in Chinese Brushstroke Painting. I knew this was a gift for an artist who has been doing Chinese Brushstroke for years – so, the pressure was on!

After debating to just simply paint the Grass Orchid onto the glass or creating the design with a layer of glass powder, I almost gave up on the masterpiece right there. You cannot reflect the one stroke technique on glass like that.

A challenge was born – I am not giving up so easily. There is only one way to go from here and that has to be 3D! I had never done 3D before – I had watched videos on the Bullseye Glass website and I knew it was a process that involves a lot of step. A lot of steps that can go wrong. Quick check of my calendar – a little over 3 weeks until Christmas, let’s do it!

The Design

Design first! I was browsing many different interpretations of the Grass Orchid online. Some were too detailed, some had a composition that would not work on a pendant at all. Quickly I decided to go with a large oval shape. Then it was time to determine the number of flowers and leaves. I remembered that 4 was an unlucky number in many parts of Asia – so I decided to stay away from groups of 4. I went for 2 flowers with 5 petals each and 5 leaves.

A design came together – step 1 done, many more to come.

​The Sculpting of the Wax Model

Next in line is the sculpting of my drawing. I decided to use sculpting wax, which I had never worked with before. So glad, that a wholesaler only sells 11 pound packages of wax. That should be enough for my little pendant project ;-)

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Problem 1: How to get to an oval that is thick enough? I printed an oval that I drew with a photo software, cut it out and traced the shape onto wax that I poured into a small container made for baking single muffins. The wax was about half an inch thick.

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Problem 2: How to carve that wax into oval shape? I found some old tools that I had for working with polymer clay. Not sure if those tools were the best option, but they worked well. It only took about an hour to get to the desired shape.

Problem 3: Transferring my design onto the wax. I have used a needle and poked through the paper into the wax along the lines of my design. So far, so good.

Problem 4: Now the difficult part – carving the actual design without removing too much of the wax. Determining the right depth of the leaves and flowers was an important first step. Then cutting everything off that is no leave or flower in determined depth. This took me about 3 hours as I was going really slowly.

​Last step was to shape all the objects. One of the petals broke off when I tried to separate 2, but I was able to glue it back on.

Problem 5: After I finished carving, I had to smooth it. I did not want to heat the wax, as I was afraid I would make it too hot and the wax would just melt. The first suggestion that I found online besides heat was using really fine steel wool. That did not work out. The wax did not smooth at all and little pieces of steel wool got stuck in the wax. Second suggestion was to use mineral spirits or naphta. As I did not have much time to figure this out, I bought both at Home Depot. First, I tried the mineral spirits on a make up remover pad. They were supposed soften the surface, but nothing happened. The naphta did a much better job. And after half an hour the wax was smooth in nearly all areas.

​Silicone Mold for Reproduction
In order to be able to reproduce the wax model, I needed to pour a silicone mold over the wax model that I just finished, hoping that this process would be completed without destroying the was model I just carved.
The silicone was not available at the wholesaler, they had to order it for me – which took over a week to deliver. Again, a large quantity – one gallon of industrial silicone – the same material dentists use to make a model of your teeth. While I was waiting for it I bought a cheap modeling kit at Michael's to see if that could help me – taking the mold did work, but the material was not usable for longer than 2 days as it got really solid and porous. The professional silicone consists of 2 parts – the silicone itself and an additive that determines the time it takes to harden. The 2 liquids needed to be mixed in a ratio of 10 to 1 and were workable for an hour. The wax model needed to be sprayed with a special mold release before the silicone was poured over it. I placed the wax into a small bowl and poured the wax over it. Then I noticed that the wax is lighter than the silicone and that it started floating. Now there was silicone on top and on the bottom of the piece. I had to remove it from the silicone, clean it, get a new bowl out and redo the pour. The silicone was a little more solid than the first time and I went really, really slowly. 6 hours later I saw that it came up a little bit, but not much. I still had to wait another 10 hours for the silicone to be solid enough to remove it from the bowl and get the wax out of it, which worked with an issue.

​Making the Silica Mold
The silica mold is the final mold that the glass will be cast into. Another 40 pound bag for just a little amount that I needed. After reading recommendations of building the silica mold with a second layer that had a grog mix added in case the first layer breaks. I did not have time to get any grog, so I decided to just build a second layer of the same silica material around the first one. The silica is mixed with water and you have about 20 minutes until it starts setting. The first thin layer is brushed onto the wax with a brush to get into all nooks and crannies.

After this dried for about 20 minutes, apply a second layer almost as thick as the first one. After 90 mins of air drying it, it is time to get the wax out. This was done with a wall paper steamer.
​I put the hose into a 5 gallon bucket and made it stand up – covered the bucket with a mesh and put the mold with the wax facing down onto the steamer. The hot steam melted the wax out of the mold slowly. After 20 minutes there was only little areas of wax left. I took the hose out of the bucket and held it directly onto the wax dots. The final wax pieces I removed with a metal tip. I put the silica mold in the kiln at 300 degrees Fahrenheit for 3 hours and left the lid open a little to dry it.

​Loading Glass into the Mold
The first thing to do is to determine the amount of glass that needs to be added to the mold. In order to do that, weigh a little cup of water. Then fill the mold with water as high as you want the glass to fill it up later. Weigh the cup again after. The difference in gram is the amount that you need to multiply by 2.5 in order to get to the weight of glass. 24 grams in my case.
I selected 2 different greens of powder for the leaves, a dark green for the stems of the flowers and 2 purples for the petals. For the background I picked white. I started filling up the mold with the colored glass in the leaves and petals. I tried to stack it up a little as I knew it will lose a lot of volume. Then I filled it up with 24 grams of white glass.
This took me about an hour.

​Time to fire
I added a bed of sand to the kiln, set the mold on top of it and leveled it with a small level.
I programmed the kiln to a really slow firing schedule, which took about 26 hours to complete. After the kiln cooled down to room temperature, I took out the mold with the glass and realized that the amount of white glass was not enough to fill the mold. The pendant was an oval shape at the top, but not at the bottom.

​So, here we go again…making a wax model from my silicone mold, making another plaster mold, melting the wax out of the mold and filling it with glass again. This time with more white – about 30 grams.

Again, level the mold on the sand bed, letting the kiln work its magic and finally breaking off the mold. This time, everything worked out well even though the mold had very fine cracks after the firing.

At least, the first pendant, that did not turn out to be oval gave me the chance to experiment with different clean up options to get rid of the plaster in all the nooks and crannies. I saw that CLR Cleaner (Calcium, lime and rust) was recommended for the cleaning, but looking at the instructions of how to use the cleaner and how not to leave it too long on the surfaces, was a little scary at this stage. I just applied some of the cleaner with a little cloth and the little plaster pieces just came off the glass.

As soon as the final pendant came out of the mold, it was clean up time and right after I was on my way to the jeweler to have the sterling setting extended to the large pendant size.He did an awesome job!