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GLASS BEAD Projection Screen

Image TIME: 8 HOURS OVER 3 DAYS Image COST: $50–$100

Need a bright surface for your projector? Get high gain at low cost using house paint and sandblasting beads.

Written and photographed by Sean Michael Ragan

Image Titanium dioxide is the most common white pigment in paint, sunscreen, and even food products. It’s cheap, safe, and almost unsurpassed in whiteness. It’s also the baseline for calculating an optical property called screen gain, which is the amount of light reflected from a projection surface divided by the amount of light reflected from a titanium dioxide reference surface. Since titanium dioxide is the pigment used in most white paint, a smooth wall painted flat white has a screen gain very close to 1.

But you can do better. This method applies a high-gain optical projection surface using common, cheap materials — flat white latex paint and glass sandblasting beads. I started out trying to directly mix them (which doesn't work) and happened on this "sprinkling" method by accident. It gives a much brighter screen surface than paint alone.

MATERIALS

» Hardboard, ¼" panel sized to fit your projected image; I used 4'×8'. Hardware stores will often cut large panels to size.

» Lumber, 1×2 (nominal), 8' lengths (4) or alternate quantities to suit your screen size

» Wood screws, flat-head, #6×¾" (30) » Wood putty

» Paint, flat white interior latex, about 2qts Plan on 2 fluid ounces per square foot of screen.

» Glass bead blasting media, 80 grit (25lbs) such as Harbor Freight item #46426. This process consumes about ¼lb beads per square foot screen area, but considerable excess is needed to ensure complete coverage.

» Drywall anchors, self-drilling, 40lb capacity, with screws

TOOLS

» Measuring tape

» Miter box and saw

» Hot glue gun

» Drill

» Drill bit, 1/8" twist

» Countersink

» Screwdrivers, slotted and Phillips-head

» Putty knife

» Dropcloth, plastic 9'×12' is a good size for a 4'×8' screen.

» Tape for securing dropcloth

» Paintbrushes, 1" foam, disposable (2)

» Paint roller

» Tub or tray, watertight large enough to allow scooping with dustpan

» Dustpan One without a lip is best.

» Hand broom or brush, medium soft, plastic bristles

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1. Determine your screen size.

Set up the projector as you will use it. Turn it on. Measure the height and width of the image. Plan the size of your screen accordingly. In my case, a single 4'×8' panel made a convenient size.

2. Build the screen.

Cut 1×2 frame members with a miter box and saw. Here’s the cut list for my 4'×8' screen.

» 2 sides 96" long on outside edge, mitered ends

» 2 sides 48" long on outside edge, mitered ends

» 2 braces 45" long, square ends

Tack the 1×2s in place on the hardboard with hot glue, then secure with ¾" wood screws every 10" or so. Install the screws from the front side of the unfinished screen, countersink them, and fill the depressions with wood putty.

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3. Lay out the dropcloth.

A plastic painter’s dropcloth will protect your floor, but it’s also useful for collecting loose glass beads after you apply the screen surface, so use a fresh one without holes. Spread it in a clean area with a smooth floor, and tape the edges down. Set your screen down in the middle.

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4. Apply the basecoat.

First paint the edges of your screen with a brush, then apply a smooth, even coat of paint to the surface with a roller. It’s easiest to just pour the paint directly from the can onto the screen — Jackson Pollock-style — then smooth it with the roller. Let the basecoat dry 24 hours.

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5. Ready the glass beads.

Pour out your supply of beads into the tub. A cheap plastic dustpan makes a convenient applicator for sprinkling. With a bit of practice, it’s easy to get an even sheet of falling beads.

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6. Apply the topcoat.

After 24 hours, paint the screen edges again, then pour about ½qt of paint onto the screen, distributing it more-or-less evenly. Roller the paint smooth. You want a quick, even, heavy coat.

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7. Sprinkle the glass beads.

While the topcoat is still wet, sprinkle beads generously over the entire surface. You'll recover any excess later, so go ahead and apply them all, being careful not to miss any spots. Once the paint is dry, the surface is hard to touch up.

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8. Brush off and recover excess beads.

Remove the excess beads using a soft brush.

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Give the screen back a few thumps to dislodge any remaining loose beads, then stand it upright for a final brushing. Peel off any flash around the edges with your fingers.

Gather up the tarp from the edges into a “sack,” and lift it into your tub. Release one edge and slowly work the tarp out from underneath the mass of beads. I recovered 16 of the 25lbs of beads I applied.

9. Install wall hardware.

I put in a row of 4 self-drilling wall anchors behind the top edge of the screen, and drove in their screws, leaving about ½" sticking out from each. Then I just hung my screen on the screw heads. It’s easy to adjust horizontally, but not as secure as I’d like. A French cleat would probably be the best solution.

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10. Hang the screen.

Put on clean gloves before handling the finished screen to avoid getting oil on it. Lift it into position and hang it in place.

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CAUTION: Depending on the size and weight of your screen, you may want to get help lifting it. Be careful!

11. Use it!

Turn on your projector and refocus and adjust the image as necessary.

Conclusion

The final surface — glass beads embedded in latex house paint — is surprisingly tough. I was concerned that flexing the screen would cause the beads to flake off, but the latex paint is still flexible after 2 years. I almost think you could apply it to a thin surface that actually rolls up.

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Another pleasant surprise was that, at viewing distances, the surface treatment is remarkably tolerant of small imperfections, and does not require a very smooth texture. I believe it could even be applied directly to a textured wall, thus eliminating the need for a separate screen altogether. Image

Sean Michael Ragan is technical editor of MAKE magazine. His work has appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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