Pumpkin Tealight Holder: SOLIDWORKS Tutorial Part 2

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Moving onto the making side of this tutorial, I put my SOLIDWORKS mold test model to use from Part 1 of this tutorial. I will walk you through the making of the mold from start to finish, I have included a list of tools and materials at the end of the blog if you would like to try and recreate this project yourself. I would note not all the materials are necessary to buy, you can use a variety of makeshift tools for ceramics, these are tools I have from my own ceramics practice.

I utilized a cake tin which has a removeable base and filled the inner seam of the cake tin with modeling clay to avoid any plaster seeping out. Then I used a mixture of soft soap and water to grease the cake tin which will make it easier to remove the plaster once its dry. I mixed 1.5lbs of plaster to 1 pint of water, and continuously mixed until the plaster began to thicken. I poured the plaster into the tin, tapped the tin gently onto the table to level out the plaster to ensure the air bubbles rose to the surface.  After the plaster had dried completely, I could flip the tin over and drop the plaster out. I did need to be very gentle at this stage not to damage the plaster, but it was also quite a tight fit. Plaster expands so be aware of this when molding with it. This creates my plaster bat. A plaster bat can be used for a range of things, but it is mainly used for drawing water out of the base of clay pieces to help dry more evenly, minimizing the risk of cracks. I’ll be using mine for a few things, including helping me to guide the pumpkin mold shape and size, and for rolling clay onto.

Choosing a pumpkin, I went with a slightly smaller pumpkin that I preferred the shape of, but I needed to prepare the pumpkin for molding into two parts. This included flattening the base of the pumpkin by trimming some of the pumpkin away like this, this will stop from it tipping over, I can flatten the base further within the molding process. I also needed to trim down the pumpkins stalk, this is to avoid undercuts in the mold, I need to keep it simple to stop the pumpkin getting stuck in the mold.

To start my mold, I used a ball of modeling clay in the center of the plaster bat, and sat my pumpkin, upright and level, ensuring it feels secure enough for me to begin sketching a mold split line. The mold line isn’t perfectly straight, because I need to ensure that I sketch over the widest area of the pumpkin to avoid undercuts. Unlike my SOLIDWORKS pumpkin model, a real pumpkin is more organic so the seam line will reflect that. Using the modeling clay, I needed to build around the pumpkin, ensuring that I don’t move the pumpkin out of place, or clay past the line. The clay will be used to create a barrier for the plaster. I used small clumps at a time and work up to the edge of the plaster bat.

Filling in all the sides, I use my metal kidney and scraper tools to scrape away the excess clay and smooth the clay out. I’m using the plaster bat as a guide ensuring the clay is flush to the plaster all the way around. This is important as any gaps, the plaster will make its way into the gaps and could pour out and ruin your mold. Then I can start smoothing the top of the clay and making it level with the mold split line. You want this to be as clean as possible as any flaws will be reflected within the mold.

An important step when molding is the create a release barrier using soft soap to stop the plaster from sticking to the pumpkin or pouring down the clay and sticking to the plaster bat. I made sure to cover the model with the release barrier and wipe away the excess with a sponge to avoid any bubbles causing holes to form in my mold. Using the thick acetate, I wrapped it around my mold several times until it felt like a strong barrier for housing plaster. This needs to be nice and tight against the clay and the plaster bat. Then using a mold elastic band, I secured the acetate into place, wrapping it around the plaster bat like this. I needed a little help for this, so my husband kindly jumped in! I also used some tape to secure the top part, and some around the acetate. Once in place, I made sure there was no gaps in the clay barrier, filling any gaps. This is again to avoid the plaster seeping out anywhere.

Pictured below is a natch maker I created with the left over plaster in my bowl, using a coin while the plaster is drying but not fully hard, I twist the coin back and forth until a concave dome is created. It works by pressing clay into the recess, scraping away the excess, and using the kidney tool, removing a clay natch to attach onto the clay like the ones seen in my SOLIDWORKS model from Part 1 of this tutorial. I scraped the back of the natch and scraped the clay where it was attached to help join the clay, you don’t want natches floating off into the plaster so they need attaching well. I attached 3 natches before moving on to mixing my plaster, I needed 4lbs of plaster for the top part of the mold.

A tip when knowing that your plaster is ready to pour, is that there will be no more bubbles floating up, and your hand will coat in plaster, rather than looking milky, the consistency needs to be a little thicker like paint. Just don’t let it do too far, as it will pour lumpy, and you may lose detail. When pouring, I pour down the side of the pumpkin so that the plaster pours more evenly and catches all the details. Banging the table or tapping mold gentle will encourage bubbles to rise out of the plaster.

Leaving the mold to set for an hour or more, I can come back and un-mold, removing the elastic band and acetate, I can clean up the top of the mold. This includes removing clay and neatening up the plaster with mold tools to have a smooth finish. While it was drying, I scraped ‘top’ onto the mold part to remind me of what way the mold needs to be. I added a chamfer to the edge, similar to my SOLIDWORKS model, and began peeling away the clay from the pumpkin ensuring the pumpkin remained in the mold.

I scraped some clay over the base of the pumpkin to tray and flatten it further before molding it. Then its time to clean up the mold with a sponge and then soft soap the mold and pumpkin. I repeat this several times to ensure enough soft soap is on the plaster. Without this plaster will fuse together and you will have a solid block of plaster.

Ready to mold the base part, I boarded up top mold with acetate, this time using clay around the bottom of the mold to stop plaster seeking out or under the mold, I added the rubber band and some tape again. I also used some clay around the edges to stop any plaster escaping, it can escape through the smallest gap, and when it starts, it can flood out of your mold, so the prep is super important. I soft soaped a final time, and then mixed 4lbs of plaster.

Pouring in the other side, the mold is done, I left this to set for a few hours before returning to un-mold.

Un-molding I added the mold alignment mark seen in my SOLIDWORKS test model to help me line up my mold from the outside. I chamfered the edge of the base mold part too, this helps when lifting the mold from the table. When un-molding be gentle and patient. My mold was then left open for almost 2 weeks to dry out.

With my mold dry, I used some paper clay and rolled it out onto my plaster bat. Then before I pressed it in, I pressed some clay into the pumpkins stalk ensuring I fill the space. The I could press the rolled out clay inside the mold. This part does not have to be perfect, but you do need to know a few things if you’ve never worked in clay. You need to look out for air bubbles in the clay, so kneading the clay and popping any air bubbles is important, the air expands and causing explosions in the clay during firing. You have to ensure you push the clay into every nook of the mold, being careful not to thin the clay.

The excess is trimmed away gently leaving a little lip above the mold for joining. I also wet the top edge to keep it from drying too fast while I repeat the process for the other side. Extra clay can be added to thicken any areas that feel thin, but you want to try and keep it the same thickness as this can affect drying and firing of the clay, increasing the risk of cracking. Each mold side is hatched with a tool and sponged with some water to hep join the parts. The mold parts are then pressed tightly together and left to set for around 1 hour.

Returning, I un-mold the pumpkin cast carefully. The marks you see below aren’t cracks, It’s the type of clay I’m using is more rough and groggy, but I can smooth these areas out with some water or slip (which is the clay mixed with some water) this can be used like pottery glue. I used terracotta clay for the pumpkins, but you can use colored clays also.  To stop them from staining your molds and subsequent castings. I used my tools to clean up the seam lines of the molded pumpkin, just scraping the clay back and buffing it out with a damp sponge.

Finally, time to use the stamps, so the clay would be too tough to cut the shapes straight through, so instead they can be used to press and print an outline onto the pumpkin.

Then I can take a scalpel and gently cut the shape out. I repeat this with the smaller star, and used a circle cutter to outline where I want to cut out a back of the pumpkin to allow for space to pop in a tealight. Removing this I can tidy up the pumpkin cuts and continue adding more star cut outs, see below.

Once all my casts were finished and dry, I start prepping them to be fired. You’ll see at the bottom of this blog my firing materials list. I used a range of things you can find at home to wrap around or onto the pumpkins to create unique colors or firing results. Firing ceramics in a ‘pit style’ firing can be very unpredictable, so its okay to just experiment. My pieces were wrapped in newspaper or foil and were placed into the furnace bin, and were surrounded by kindling, wooden logs, straw, sawdust and newspaper balls. It was then lit with matches from several different points around the bin, to try and encourage an even firing.

Don’t overload the firing, two to three pieces should be enough for a bin this size. You should also try to pad out the pieces well as they may fall onto each other and cause breakages. You want to keep the pieces quite low in the furnace too, to avoid them dropping and cracking. The fire should burn as evenly as possible and for as long as you can within the bin, so use plenty of logs where you can to keep the fire going. The lid of the furnace was put on as soon as the fire seemed consistent. Then it was left until it was fully cooled down before I could remove my final pieces. If you remove the ceramics while they are still hot, this again can cause breakages to happen as the clay would cool too quickly.

I did have some breakages myself, which is to be expected with ceramics, so don’t be disheartened. You should be able to tell if the pieces were fired hot enough as they will make a clinking sound when you tap them. Below are my final pieces.

 

Materials & Tools List for Mold

  •          12cm in Diameter Pumpkin
  •          Black Flexible Plaster Mixing Bowl
  •          Modelling Clay 1150 3kg
  •          Soft Soap 500ml
  •          Metal Steel Kidney 13cm X 0.038cm
  •          Potters Plaster 10kg
  •          Roll of thick Acetate
  •          Mold Elastic Bands
  •          Scales
  •          Water Jug
  •          Round Baking Tin 18-20cm (with removable base)

 

Materials for Modelling

  •          3D Printed Stamps
  •          Banding Wheel
  •          Scalpel
  •          Potters Tools
  •          Sponges
  •          Rolling Pin
  •          White Raku Clay 1kg
  •          Terracotta Body T.S Flax Paper Clay 5kg

 

Materials List for Firing

  •          90 Litre Galvanized incinerator bin
  •          Kindling
  •          Straw
  •          Wire / Chicken Wire
  •          Newspaper
  •          Banana skins
  •          Foil
  •          Salt

 

Plaster Mix Ratios

WATER IN PINTS PLASTER IN LBS
1 1.5
2 3
3 4.5
4 6

 

Jade Wilson

Jade Wilson

I am a 3D Designer and SOLIDWORKS Blog Contributor from the UK. I am a self taught SOLIDWORKS user, and have been using it to inform and create my designs since 2012. I specialize in the design of Ceramics, Home Accessories and Wooden Toy Design.