How old was the cast when the test was done?

I have found a fresh cast, and an identical one a couple of weeks old, have very different performance. For example; casts on plotter vellum work very well when fresh, but after a few weeks their brightness fades to about half. And a cast on 320 grit sand paper left horrible trails at first nice aged to bright blobs without trails. Over a few weeks its blobs start to fade, this drove me nuts when testing many different textures!

Ideally, you want a fresh cast to have a slightly too slow release (fading trails) so that it will mature to bright blobs with no trails. I’d guess this has some dependencies on the specific resin (I’ve been using Elastosil M4641), but suspect all do it to some degree. I’ve tried some “hot” casts, with slightly more catalyst, still the same. Something to keep an eye on…

Retest it after a few weeks.

Great video!

How did you plan on attaching this new silicon fabric to the acrylic, were you just going to lie it down on top?

I just cut the finished piece out with a razor blade. I use the same piece of nylon a few times, then it gets a bit of silicone in it and looses some of it’s texture.

Just this evening I tried another fabric. It has a weave about like canvas, but I think it’s a polyester fabric. It works quite well for texturing silicone. It’s curing now.

I clear coated the top of the sheet I made in the video. Bad idea. It lets too much light through the paper and it looses some of it’s diffusion properties. Better to just leave it as is and cover it with a sheet of 5 mil clear mylar. I chucked it in the bin.

This is just RTV silicone from the hardware store. RTV stands for Room Temperature Vulcanization. It cures rather rapidly here in the tropics due to the high humidity. In a dry place like Arizona, it cures much slower. It produces sticky, lingering blobs at first, but a few hours later they settle down to nice bright blobs with quick release. I’ll be testing this stuff for weeks to come. It’ll be interesting to see how it holds up.

As far as attatching the siliconed sheet to the acrylic goes, I have a margin around my image area where I simply tape it in place, slightly taught.

diy is the key , waiting for a video of the final results !

keep up the good hzck !

OK it’s a late night here in the home lab.
I shot two videos of the new surface. This is a sheet of drafting vellum, with a layer of textured silicone on the down side. The upper side is plain, uncovered vellum.

It’s REALLY sensative. I am extremely pleased with this particular fabric I used to get this texture!

First, here’s what the IR cam sees:

You’ll love this demo.

Ok. This looks awesome!

So your layers are from top to bottom:

velum (projection surface)
textured silicon
acryl

?

So what fabric did you use, or what texture? Rather rough or a very fine ?

Really amazing results. The best i’ve ever seen.

Thats really cool. I shall try this once i get mine built.

Great job, Tinkerman. This could be very useful specially for those who can’t find Sorta Clear 40, like me. My team got impatient and tried to replace the Smooth On product with RTV silicone, and the result was not pretty.  This may be a good alternative.

Just one thing, is drafting vellum the same thing as sketch or tracing paper?

Hi Tinkerman,

so you made multiple layers of silicone, but they are still altogether very thin. So i guess the multilayering gives a better structure and is less “sticky”?

Excellent! This is a good step forward. We also have been using various techniques to get the layers to unstick, but we did not try bonding the silicone and cloth together.

Also curious to try out the textured approaches. Won’t that show up in the projection though?

Drafting vellum is just really good quality tracing paper. It has a smoother finish and it diffuses light more. This set up is working great as a projection screen as well.
Really bright, no hot spot where the projector bulb is and very crisp and clear.

The fabric I used is about 80 threads per inch. I think it’s Dacron. It’s not stretchy. It’s a rather stif weave, which is good.

I built the silicone up in two layers on this sheet. The first layout is very thin. It only leaves about .005” of silicone. The second layer goes on much better because of the texture created by the first layer.
It lays out very even and leaves a nice texture. It almost looks crystaline in the light! Beautiful!

The enitre layer of silicone and vellum measures perhaps .020”. Not very much, but plenty to do the job.

It’s all these micro bumps that make the nice blobs.
When they are pressed against the surface of the acrylic and deform slightly, they bump into each other and fill all the voids thus refracting that wonderful IR glow.

This a a strip I cut away from the edge of the sheet, close up.

Is there any way you can get a picture of the silicone side? I’m wondering how clear it is. Like rogerj said above, be ready for some changes in the response over time. We tried about 15+ textures, and most of the ones that worked well the next day, didn’t work well after a few weeks of fully curing (hopefully you won’t have that issue though). It would be nice to see how this compared to bonded silicone on your same table (side by side) to see the true difference between the textured and bonded silicone.

Tinkerman, have you tried not casting on the vellum directly and just making a texture on the bottom side? This will allow for a free-floating silicone that can be used with any projection material on top.

Here’s a video of some old tests comparing textured silicone.

This test shows the difference between bare acrylic, plotter paper textured silicone, and frosted polycarbonate textured silicone. This video was made about 2-3 weeks after the silicone was poured. The plotter paper used to work very well right after it was curred, but after the 2-3 weeks, it barely worked at all. The frosted polycarbonate which left huge trails worked with very little trails (and since videoing shows just about no trails).

Keep in mind that I’m using half the amount of LEDs as tinkerman so the blob intensity will not be the same.

I’ll post some more videos later that compare bonded and textured silicone.

ADDED: The above test was used with “Elastosil M4641” silicone.

Cerupcat, are you using Sorta Clear 40?

@ GFantini: I updated my post. That was using “Elastosil M4641”

@ Cerupcat

That pic is silicone side up. What you’re seeing there, starting at the right is the first layer of silicone that was outside of the textured area, the textured silicone, then the textured silicone on the white vellum. The bare side of the vellum is facing away from the camera.