Selective Dispersion of Projected Light - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 36 Old 01-19-14, 02:16 AM
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Re: Selective Dispersion of Projected Light

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Don,

What do you think about using Valspar Clear Protector in a flat sheen?

I was also thinking that I could incorporate some very transparent pigments to make a very translucent neutral gray that would still get down to the vertical grooves still get some selective dispersion of the light. I'm not too familiar with the Behr Faux Glaze so just wondering if that would allow mixing in of other acrylic based pigments. Also concerned about the sheen for Behr Faux Glaze.
Yes, the Valspar product will probably work better than the Behr, I just didn't know it was still available.

As for making a truly transparent neutral gray I would probably use a black watercolor paint. Dick Blick has a 'student' series called 'Blick Liquid Watercolors' that won't break the bank.
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post #22 of 36 Old 01-20-14, 09:33 PM Thread Starter
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Re: Selective Dispersion of Projected Light

Did some more experimenting today. Went back to the idea of brushed metal. I purchased a small 6" x 18" piece of aluminum sheet. I brought this home and started with 120 grit sandpaper and a sanding block. I ran the sanding block along a board used as a jig to keep the motion of the block linear. I moved on to 180 grit paper, followed by final passes with 320 grit sandpaper. I brushed a 6" x 6" area of the panel...so I have more to test with in the future.

For a top coat, I used Rustoleum Polyurethane Matte as the base (couldn't get VCP in flat). I also purchased pigments at Michael's from the Golden Paints Fluid line. The pigments are: 1. Ultramarine Blue (PB29), 2. Quinacridone Magenta (PR122), 3. Hansa Yellow Medium (PY73). I chose these pigments as they are very transparent and should allow color-filtered light to get down to the aluminum.

I mixed a very small batch using 30mL of the Poly Matte, with 17 drops of Ultramarine Blue, 3 drops of Quinacridone Magenta, and 4 drops of Hansa Yellow Medium. This mix very roughly represented a transparent gray. I'll admit that it still needs a lot of work to get it neutral.

I then rolled on 2 coats of the mix onto the brushed aluminum and let it dry.

Here are some results:

Approximately 30 degrees horizontal off center:


Approximately 70 degrees horizontal off center:


Approximately 30 degrees vertical (below) off center:


There was a small desk lamp turned on and located to the left of the screen. There was also a bit of ambient light from the outdoors with light curtains at mid-afternoon. I took the photos off to the right of the screen (or below). [EDIT...The projector is table mounted.]

The left image is on the painted white wall (matte paint). The right image on the brushed aluminum with topcoat. To the right of the brushed aluminum is the raw aluminum sheet.

Observations:
The aluminum still comes through too strong and I can see the vertical grooves in the metal. See the pics of the woman where it is more pronounced. Off axis in the horizontal cone is still good out to about 70 degrees. The vertical cone is very small, maybe 20 degrees.

I have gone ahead and applied 2 additional coats of the same mix (total 4 now) and will get more photos when time allows. I think it needs to get the proper coat thickness for the matte to just hide the vertical grooves.

Last edited by Pyrometman; 01-20-14 at 11:13 PM.
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post #23 of 36 Old 01-21-14, 02:38 PM Thread Starter
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Re: Selective Dispersion of Projected Light

I looked at the sample quickly this morning and it still appears to have significant sheen even after 4 coats despite being "matte". Is there something better out there, perhaps the Behr Faux Glaze mentioned earlier. Would one of the Valspar tint bases work better to get cut the sheen down. It looks like Valspar Base C has not titanium dioxide in it. Would something like that work better? Also does anyone know the order of the latest Valspar finish names in terms of sheen?
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post #24 of 36 Old 01-21-14, 04:35 PM
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Re: Selective Dispersion of Projected Light

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Pyrometman wrote: View Post
I looked at the sample quickly this morning and it still appears to have significant sheen even after 4 coats despite being "matte". Is there something better out there, perhaps the Behr Faux Glaze mentioned earlier. Would one of the Valspar tint bases work better to get cut the sheen down. It looks like Valspar Base C has not titanium dioxide in it. Would something like that work better? Also does anyone know the order of the latest Valspar finish names in terms of sheen?
The sheen could change (get less) slightly over a week or two as the paint cures, but it would be slight.

Yes, the bases designed to make darker colored paints would be "clearer" since they would have less (or no) TiO2 in them. This is something I have always meant to check into deeper, but haven't. I know when I first got into DIY screens I got a can of the blackest paint ACE hardware sells and watched the guy mix the color. The base was quite clear and the guy said he had to actually add a bit of WHITE tint to the can so the paint would cover other colors better.

The Valspar Signature paints, in increasing gloss level, come in Matte, Eggshell, Satin and Semi-Gloss. More details for them can be found here.

We really haven't spent much time looking into clears since Mech did his testing. Every one we have tried so far has added yellow to the mix that deepens in strength as it ages; but there MAY be a good one out there somewhere. I highly suspect it would be one of the clear mediums for artists.
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post #25 of 36 Old 01-21-14, 05:02 PM
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Re: Selective Dispersion of Projected Light

Hmmmm, your results are certainly interesting. It makes one wonder what effect going to 600 or 800 grit sandpaper would do.

I just tried to find the gloss rating of Rustoleum Polyurethane Matte and it isn't given for the product. When I checked Behr Faux Glaze is says it isn't applicable.

While you are certainly free to use any colors you want to to try and make a neutral gray I do feel the need to mention that there is no reason whatsoever to use an RGB or RGBY mix to do so. While I suppose it could be done, I know it can be done easier and better using black, yellow and red tints or pigments (usually Yellow Oxide and Red Oxide). In both Color Science and painting for artists it is a known fact that the more colors used make up a black the "muddier" it gets and the color ends up a dark brown or other color.

If you want to make the screen mix a bit more opaque I would try adding some Zinc White (sometimes called Transparent White depending on paint brand). This white isn't as "covering" as Titanium White.
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post #26 of 36 Old 01-24-14, 02:41 PM Thread Starter
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Re: Selective Dispersion of Projected Light

Don,

Been a few days. Just been busy with other things butI haven't dropped this. I was going to do exactly what you suggest with finer grit sandpaper, perhaps even going to 1200.

As for the topcoat, I found an MSDS for the Valspar Signature Base C that shows there is only 0.1 to 1% TiO2. I think that I'll give that a try in Matte finish. As for tinting that base I could do two versions. One using the existing pigments I already purchased, and another using black/red/yellow as you suggested. I want to hold off on using zinc white for now as I want to rely on the aluminum as the reflector. My only hangup using the black/red/yellow was that I couldn't find a black that was transparent enough. I used the transparency ratings from the Golden Paints products but their blacks are much more opaque than the pigments I settled on. I really want to get the light down to the aluminum to maximize the selective dispersion.

I think I may have to set up an experiment that varies the pigment loading to find what works best. At this point I am not sure where I should be with regard to the loading. I need to think on that a bit more.

Last edited by Pyrometman; 01-24-14 at 10:29 PM.
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post #27 of 36 Old 01-24-14, 07:57 PM
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Re: Selective Dispersion of Projected Light

I believe that water color paints are more translucent than water-based acrylics, but I have not done any personal testing for that. The best thing to do would be to use colored dyes instead of colored pigments as the dyes use much smaller particles to produce colors.
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post #28 of 36 Old 01-25-14, 05:10 PM Thread Starter
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Re: Selective Dispersion of Projected Light

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I believe that water color paints are more translucent than water-based acrylics, but I have not done any personal testing for that. The best thing to do would be to use colored dyes instead of colored pigments as the dyes use much smaller particles to produce colors.
Don,

Did another experiment today. This time took the sanding to 1200 grit. For the topcoat, I purchased a quart of Valspar Ultra Base C Flat. To color it, I went with your idea and used a product called Jacquard iDye Poly in black. The dye comes as a powder. I used 1/4 cup of water, and 1/4 tsp of the dye and mixed. I then used 15mL of the Valspar Ultra Base C and mixed in small amounts of the liquid dye until I got to a gray that I liked. I then painted two coats onto the aluminum.

Results:
The Valspar Ultra Base C Flat completely hid the grooves in the aluminum. It's just too strong as a diffuser. I didn't even bother to take pics as it just looked like a flat gray paint.

Perhaps a mix of the Valspar Ultra Base C Flat and some of the Rustoleum Matte will give a better blend of diffusion and transparency.
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post #29 of 36 Old 01-25-14, 08:36 PM
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Re: Selective Dispersion of Projected Light

Cool! Please keep us posted on your trials. Getting a paint with just the right amount of transparency, light dispersion and grayness will be a challenge.
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post #30 of 36 Old 01-27-14, 09:45 AM
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Re: Selective Dispersion of Projected Light

For transparent paint that doesn't yellow, I've heard Darmar varnish from Michael's (used for protecting paintings) holds steady despite the evils of time and UV. I think thinner paint rather than more transparent paint might help, but that would still probably require wider micron valleys, especially if a more shallow angle can cut down visual artifacts of a grooved surface.

I have an old highgain gray screen that appears to use a gentle wave pattern in a very similar fashion to your current experiment, but instead of high gloss it uses reflective particles in the paint (looks just like mica based metallic). It works well with the ridges widening the viewing cone very nicely while the vertical limits are still tight and making efficient use of the light that's projected while deflecting overhead lighting to the floor rather than diffusing it around and making itself a lighter shade.

If you find a suitable way to DIY a grooved screen as you've planned it'll make my day as I've been scratching my head about how to properly brace a solid curved screen and your alternative tackles the same issues without the problems of a curved screen!
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