Introduction: How to Plaster Cast a 3D Printed Sculpture on a Budget

By Discover our open source museum
About: Scan the World is an ambitious community-built initiative whose mission is to share 3D printable sculpture and cultural artefacts using democratised 3D scanning technologies, producing an extensive ecosystem o…

We are Scan The World a non-profit, open source and community built initiative whose mission is to share 3D printable representations of cultural artifacts in a remarkably tangible way. You can enjoy around +18000 .stl files of cultural artifacts freely available on our website.

New 3D models keep coming to our collection day by day thanks to the help and support of our community. For this and many other reasons, we like to define ourselves as an open source museum with no barriers!

All of our objects are optimized for printing and you might be wondering “What can you do once you 3D print a sculpture?”. Well, there are infinite options, but today we decided to show you how to plaster cast a 3D printed sculpture on a budget. In our case we decided to use a 3D printed bust of Costanza Bonarelli, the dimensions of the bust are 40x35cm but this tutorial applies to any sculpture of any size.

If you want to know how to do it yourself, at home and on a budget, keep reading!

Let’s dive into it!

Supplies

  • Plaster from Paris (approximately 8 kg used for 40x35cm 3D print)
  • Alginate (approximately 7 kg used for a 40x35cm3D print)
  • A smooth plastic container big enough for the object
  • Washing up liquid
  • Old newspapers
  • Craft knife
  • Blu-tack
  • Mastic
  • Ready-mixed filler

Step 1:

Choose the right size casting container: the object should fit perfectly without leaving too much space around.

Step 2:

Lubricate the interior of the container with washing up liquid, which will act as a release agent.

Step 3:

Fill in any hollows present on the original object with old newspapers to prevent the alginate from damaging it (in our case we covered the base of Costanza’s bust).

Step 4:

Mix up the alginate powder with water as indicated in the instructions of your product of choice. Be fast and mix vigorously as this type of material tends to set fast.

Step 5:

When ready, pour the liquid alginate in the container around the object, trying to hold the object still while pouring.

Step 6:

Leave the alginate to set.

Step 7:

Once set, run a craft knife around the rim of the container to start detaching it. Flip the container upside down delicately, the washing up liquid will help the mould come out smoothly.

Step 8:

Carefully slice the alginate vertically in order to reveal the original object. The alginate material has now taken the shape of your object. Remove the original object and place the alginate back inside your container to act as a mould for the next steps.

Step 9:

Mix up the plaster of Paris ready to be poured into the negative space of the mould.

Step 10:

When the plaster mixture is ready, it will usually have the consistency of double cream. At this point you can pour it inside the mould carefully and let it dry.

Step 11:

To avoid air bubbles forming, gently rock and tap the container so that any air bubbles within the wet plaster are forced into rising to the top.

Step 12:

Leave the plaster to set for at least 30 minutes.

Step 13:

Invert the container and carefully extract the mould. Attention: if the object is big, it will be very heavy at this point.

Step 14:

Carefully peel the alginate to reveal the cast inside. This also reveals two vertical lines running around the object, the so-called “flash lines”. These lines indicate where the two halves of the alginate sat next to each other during the casting process, they can be easily smoothed out afterwards.

Step 15:

The 3D printed bust of Costanza Bonarelli is a big object, therefore the bust was split in multiple parts and the above steps were repeated for each part of the bust. When it came to casting the breast of the figure, the extremely detailed relief had to be covered with some blu-tack. Undercuts on high relief areas such as this can often cause the alginate to get stuck and tear away during the de-moulding process. Using the blu-tack to cover those parts prevented this from happening.

Step 16:

After casting all of the object’s parts, let them dry overnight.

Step 17:

Stick the parts together (if applicable) by using mastic.

Step 18:

Finally, smooth out the plaster cast with lightweight ready-mixed filler and remove any existing cracks or bubbles that might form during the process.

Step 19: Your Plaster Cast Is Now Ready!

Thank you for following this tutorial kindly directed by Abbey Ellis for Scan The World, please share with us your creations!