Introduction: Building a Magic Pensieve

About: Web developer by day. Gamer by night. Halloween fanatic and DIYer, all the time! My projects tend to combine pop culture, technology, and craftsmanship to produce something that's fun, unique, and more than l…
This project accompanied several others for our Harry Potter themed Halloween party.


The Pensieve is a magic device which plays a significant role in the Harry Patter series. It allows one to revisit captured memories - either of their own, or from someone else. Various key plot points are revealed through the pensieve as Harry experiences the memories of several other characters. Through the Harry Potter movies, Dumbledore's pensieve takes on a couple difference appearances, but I wanted to stick close to the book description of an ornate stone basin - this agrees with the film version in "The Goblet of Fire", and is also the style it's portrayed in at Universal's Wizarding World theme park.


I wanted a way to view photos from our past Halloween parties in a large bowl of water. Actually submerging photographs wasn't nearly cool enough, so I decided I'd place an LCD display below the bowl and run a gallery of photos in slide show mode. I tried all kinds of orientations and even considered using mirrors, but using a laptop wouldn't let me achieve the pensieve/cabinet shape i was after. So I decided on using a separate LCD monitor inside the prop and an external laptop to run the slideshow.

Step 1: Materials

Here's a rough list of materials I used to build the Pensieve:
  • A 19" LCD monitor (4:3 ratio)
  • A laptop to drive the monitor
  • A large clear bowl
  • An ultrasonic water mister
  • A couple 2x4" boards
  • approx 4 sq feet of thin plywood
  • approx one sheet of 1/2" foam insulation
  • liquid nails and some screws
  • 3 mirror panels (30" x 8")
  • various bits of wood trim
  • paint (white and gold)
The first important step was finding the right bowl. Luckily I just happened to already have something that was perfect. It was clear, about a foot in diameter, and (very important) had a small lip around the top. Even the design around the sides was a simple pattern of ridges that would give a nice distortion effect to the edges of the photos. Then it was a matter of pairing the bowl with a good sized LCD. Again, I was lucky to have an old 19" non-widescreen LCD which matched up nicely.

Step 2: Building the Pensieve Top

Using thin 1/4" plywood, I cut out the top of the pensieve. The shape itself is octagonal, but I would be adding some mirrors behind it so I left the back end square for building onto. I had to make sure to size this octagon large enough that the monitor would fit inside. Then I cut the hole the bowl would sit in, making sure it was slightly smaller than the lip of the bowl.

Then underneath, I made a little shelf (really two L-brackets) for the monitor to sit on. This had to be low enough the the screen would sit just below the bottom of the bowl. At this point I was able to plug in the monitor and fill the bowl with water, for a simple test run to check the effect, alignment, etc. Everything looked really promising so I pressed on...

Step 3: More Framing and Covering

From there I added a simple frame to stand the pensieve up. It had to be sturdy enough to hold the monitor, a large bowl of water, and perhaps some pressure from someone leaning on it. I wanted the basin to appear to be supported from the wall, so I kept the bottom of the stand pretty small, but large enough not to be tipsy.

The monitor easily slides into the shelf and needs no hardware to secure it. The bowl could have been sealed down with silicone caulk (to protect the monitor against any spills), but I opted to just set it in place which makes filling and emptying the water super easy.

Then I built out the other sides of the pensieve with pieces of rigid foam insulation and liquid nails. Seams were caulked and everything was sanded, then painted.

Step 4: Making It Fancy

The pensieve needs to have some grandeur to it so I started adding decorative details. Etched pieces of wood trim were added to the top surface, and trim molding around the sides. A miter saw was so useful here! Everything was attached with liquid nails (no nail holes to fill!) and the seams were caulked as necessary.

Then I added the background wall which would support mirrors behind the pensieve. This also gave the whole thing some nice height making it even more dramatic. I used 1x2s to frame the three back sides of the octagon. Aluminum channel was cut and attached to securely hold the mirrors. Some more insulation board was added to cover the sides and bottom of the stand, and then everything was painted.

After the paint, the mirror panels were added (they were actually available in this size in the bathroom department of a home improvement store), and some wood applique pieces were painted gold and attached to finish the flair.

Step 5: A Final Dose of Magic

The monitor running a slide show under the water looked pretty good, but it needed something more to make it come alive. I thought about occasionally tossing dry ice in the bowl, but that would require a little attention during our party. So then I realized an ultrasonic mister would be great. Not only would it constantly produce a low lying, foggy mist, but it also gently churns the water so it's always in motion which helps brings the photos to life. Another bonus is that it has a series of LEDs which cycle through different colors. When you're a few feet away, you can't see the photos, but the LEDs still cast an eerie glow across the room.

I tried various positions for the mister, including somewhere completely hidden while venting the fog to the bowl, but sitting it right in the center of the bowl was by far the best. Sure, it blocks a bit of the image underneath, but between the fog, the rippling water, and the glowing lights it's well worth the trade off. Just filling the water level to about an inch above the top of the mister and I was in business.

I was very happy with the final result. It's a decoration that's both dramatic and engaging - guests would walk up, lean in, blow the fog away, and view the memories of Halloweens past.

Halloween Decorations Challenge

Finalist in the
Halloween Decorations Challenge