Introduction: Generate a Unique Shadow Casting Sculpture

About: Experimental physicist

This instructable will teach you how to cast intricate shadows using very cheap (free) software with simple tools (like lofting). The first image above reveals my goal, that is design and print an abstract object that casts an unexpected shadow. In summary:

Real thing-> abstract silhouette
really abstract thing-> real shadow

The second image above provides examples of what other artist created using just raw talent. Their art is amazing, and I wished to duplicate some of their results for my own wall, and this instructable is a result of that primary attempt.

Although I list their webpages in the image, here are direct links to get you excited (but you’ve got to come back):

For thoroughness, I want to mention two other people:
TheJehosephat: created a shadow sculpture Instructable without using software.
Ryan Meuth: his version of a 3D printed “shadow caster”. I’ll talk about this in step 7.

These artists have incredible spatial acuity and do quite a bit of planning and then quite a bit of tweaking to get things just right. On the other hand, using just one or two pieces of free software, and either a 3D printer, laser cutter or just cardboard and a knife, its quite easy to create your own abstract piece of art that casts a realistic looking silhouette. Plato’s cave dwellers would be so proud.


-of course paid CAD packages work as well (Inventor, SolidWorks, Rhino,.....)

  • *Rapid prototype printer or service, or even better, cut it out yourself using 123D Make

I wanted to only use the free 123D suite of software products, to keep things simple, consistent, and fun.
Here is a link to the published file in their gallery:

Step 1: Determine Your Subject

The most difficult part is choosing what you want to display. I decided on this snapshot of two boys trying to knock each other off a pedestal. They almost make a heart shape with their bodies in the process (love and war takes many forms).

The silhouette must be converted into an outline for this to work. I am sure that other methods exist in other software, but I took the brute force approach and traced it. The background can be removed using Apple’s basic Preview (select->instant alpha) or Adobe photoshop or similar, but this is an optional step. In my case the resulting image was imported into 123D by placing it onto a canvas, and I manually traced around the important parts using the sketch->spline tool.

You will want to end this sketch and start any new drawings separately.

The Work Axis lines (Red) are discussed later.

Step 2: Determine Your Light Source

Before making your shadow casting object, you must decide where your light will come from. This can be an indoor ceiling light, the sun, or even a portable flashlight. I decided to use 123D Catch to model my utility flashlight as though it is my light source. I did this for a few reasons: It demonstrates the ease at which you can import a scene into 123D, and it makes scaling your shadow and generated objects much more tangible. Having a physical entity for scaling and positioning provides such a benefit that I can not emphasize it enough.

Video instructions for using Catch can be found here:

Basically, it takes snapshots from any camera source (I deliberately used my terrible resolution phone camera), and stitches them together into a mesh form and applies your image based texture. Its really easy and intuitive. If the software has problems, you can manually make changes to the pixel points that should match. The crazy path that the video seems to take is just the vantage point from which I happened to take the photo. This can be edited if you desire.

  • Lasso the parts you care about and export as an .obj
  • This is very important and necessary if you want to import into 123D.

Once inside 123D, its a matter of scaling and positioning your sketch relative to the light source to create your lifelike environment. The cool aspect of this approach is that the exact size and position of your sketch will have the same relative size and position in real life.

It should be noted that you can perform this in the reverse order. 1st make your scene and then 2nd create your canvas and sketch.
For those of you that are exceptionally keen, I did not scale my flashlight scene before exporting and therefore the scale in 123D is too large in these images.

Step 3: Copy, Paste, Shrink, Loft

Every part of this instructable leads to this step.
If the sketch that you made from tracing or otherwise is copied, it can be used to create a solid feature. This copied sketch is pasted onto another parallel plane, then shrunk and positioned inside the guide/working axes. The reason that a duplicate sketch is used instead of a point, is that even though your light may be approximated as a point source, lofting doesn't like it.

Guide lines are produced starting at the light source and leading back to the original sketch (the shadow). I simply created a point in space that aligned with the utility flashlight bulb and connected itto points on the edges of the sketch using Construction->Work Axis-> Axis by Two Points.

Four lines are enough, assuming they are at the farthest, nearest and widest parts of the sketch.

You may think that projecting a sketch onto another surface will work, but only if your light source is the Sun in which you can very easily approximate the rays as parallel. For far away lights, this is also true, but your shadow may be blurrier.

Step 4: Combine Through Intersection

Lofting in 123D can be very simple. I first was very confused because the program thought that my sketch was a path. If you see a starburst like icon next to your sketch and it has anything other than **profile** in the text box, then click the star and select swap. Then everything should work just fine. Don't forget to use the OK operation to complete the Loft.

I'll show exactly what the sequence should look like in the "What Not To Do" step, but if you understand the Combine operation, then you can jump right in.

Step 5: Modify Artistically

You now have a shadow casting solid that you can export as a .stl for 3D printing or cutting (123D Make).

But no sense stopping here. This could be the best part. Now I don't claim that this example version is the most elegant. It happens to go with the decor already present in my dining room. The idea is to disguise your solid so that its purpose isn't immediately obvious. At least I wanted mine to have somewhat of a mystery about it. Otherwise why not just tape a one sheet paper cutout to a piece of plexiglass and create a shadow that way?

I used rectangles, spheres, cones, and my favorite, a torus, to take away bits and pieces of redundant material. Remember that as long as you maintain a sliver of the profile somewhere along the ray's line of sight, the light will be blocked.

Step 6: Make Your ShadowCaster and Silhouette REAL.

After you are satisfied with the final shape, you must ensure that it is one piece. You can do this using the Combine->Join operation. If you only cut away from one original shape, then this step is unnecessary. I added an additional post so that it will appear my boys are jostling on a balance beam instead of mid-air. Therefore I need to join those two pieces.

Export the single component as an .stl (You will need to login to 123D to use this feature)

Upload your piece to any number of rapid prototyping services, or if you can, print in on your own 3D printer. If you use 123D Make, then you can cut out slices with a laser cutter. If you are tedious enough you can print it on a traditional boring printer and cut out the shapes yourself.

But by all means,
PRINT this thing somewhere! Mine is on its way.

Oh, and make your friends guess what it is before you turn the light on. They are always very surprised at the results!

Step 7: What Not to Do

Suppose you want to make a single object cast three distinct shadows from three light sources or from changing the angle of just one light. Two of the artist's mentioned in the introduction have such a sculpture in their portfolio. If you try to do this in software, you must be aware of some pitfalls.

Take for example the drawing in the first image above. It shows three sketches on orthogonal planes. If you go through the previous steps, you might start off like the second and third images reveal. Notice the use of OK to complete the Loft and Intersect operations. And do you see the orange starburst with the text Profile 2 next to it as mentioned earlier?

Without a starting material, you will end up with nearly nothing after all three lofts are Intersected (see the 4th image in the above sequence). So that's not the right approach.

If you intersect with something large (5th image), then you will have something to print, but it won't give you the right shadow. Here, in passing, I give a quick route in the 5th image to get to the Intersect command Right Click->Solid Features->Combine->[change join to intersect]. Doesn't sound quick when you type it like that does it.

The problem comes from the multiple lofts not intersecting each other along overlapping axes. They must cross. Even if you use a different starting volume, like another polygon, it looks pretty, but you won't have the right shadows.

So Start simple. Then work up to multiple shadows and alternate starting volumes. If you want to make it out of wire, like some of the other artists, make the wire first. Then remove them with the loft as before. Enjoy.

And please post your shadow casting models in the comment section.

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