Not to get long winded and overly technical, but…

You have to consider elasticity _before_ hardness.  You want softer AND more elastic for “zero-force”.  You want it to spring back faster when you lift your fingers to prevent “ghosting”.  Lexel is a mixture of Silicone and Latex.  The Latex makes it snap back faster than pure silicone alone.

From the PDF Brochure:

Hardness, Shore A 25 (30-day cure)

Tensile Properties
@ 50% stretch Lexel has a 96% recovery in 1 minute
@100% stretch Lexel has a 96% recovery in 1 minute

Toughness
No additional tearing at 200% stretch (knife cut made in Lexel
perpendicular to stretch)

Sorta Clear 40 from a technical PDF:

Shore A 40
Elongation At Break . . . 400%
100 % Modulus . . . 90
Die B Tear Strength . . . 120 pli
Shrinkage . . . . . Negligible

What I can decipher from the technical jargon (and my own testing) is that the hardness you seek is really the “snap-back” quality.  This “toughness and tensile strength” that Sorta-Clear advertises is worthless for our application and the hardness is worse, not better.  If the compliant surface is suppose to simulate the frustration caused by a finger on acrylic, then a Latex + Silicone mix is much more like skin than Sorta-Clear or pure silicone. Simply put, you don’t need to press as hard with Lexel.  Also, the refractive index of Lexel is _WAY_ closer than Sorta-Clear to the refractive index of the acrylic. Evanescent wave coupling requires similar (or identical) electromagnetic properties between two separate layers.  I _highly_ doubt the PLATINUM in the Sorta-Clear 40 is encouraging a good coupling on the electromagnetic spectrum.  This means a slightly brighter blob, but it also significantly lowers the total internal reflection by allowing more and more IR light to refract out (illuminating your projection surface increasing the backwash glow), which means it is _NOT_ truly scalable.  The larger the surface, the farther from the edge illumination, and you will have dead spots with no illumination or very weak illumination.  This may be at ridiculous distances, but the math supports it.

Personally, I just wish fiducial markers were easier to see through the Rosco Grey! I think I might print them out using IR-reflective ink. But I digress…

I redid my silicone layer this weekend and recorded my experiences.  i havent tested it yet, but I think it turned out much better.  I was more careful with the preparation this time. 

I kept the silicone caulk/toluene solution thicker this time.  The layer dried much quicker and is about twice as tick as my first one.  It seems very hard but rubbery and springs back to shape quickly.  The new layer also does not stick to the mylar like my first layer did.  I will get back about the turnout once I get everything put back together.

All in all this really wasn’t that hard.  It took about 2 hours including all preparation and I was able to do it in my fiances bedroom.  I hope it turned out good, it is certainly cheap and relatively easy.

If this doesn’t work out nicely I might try to get my hands on some of the LEXEL Adam has been talking about.

Adam:
When you wash your layer with toluol to make it even and clear. To you angle the screen and let t run down?  Or do you wipe it with something.  I tried wiping with various materials on a spare piece, but whatever I used to wipe seemed to ruin the surface.  Do you let it dry again after after applying the toluol?  For how long?

Im wondering whether this works better with the LEXEL you talk about.

thanks alot.

Angling your acrylic will cause rippling as some parts of the softened Silicone/Lexel will dry faster than others.  Use gravity by keeping the acrylic completely level. I used small amounts, repeatedly applied every 15 minutes to a half hour, for a few hours.  I was tempted to soak the acrylic in a shallow pan to soften the Lexel, but using that much toluene at one time over that large of a surface is just plain stupid and dangerous.  I am really tempted to adhere the Rosco directly to the acrylic using a softened layer of Lexel I could use a rolling pin or a scraper/rail-guide to undo ripples, but I don’t know how easy it would be to undo/redo/fix if it didn’t prove optimal.  I may purchase more large pieces of acrylic for testing soon, we will see.

**NOTE: if trace paper, Mylar, or Rosco sticks to your surface, it hasn’t finished curing properly.**
***IMPORTANT NOTE: Most tape adhesive will react with the toluene badly. Be careful, or find another method.***

This makes sense.  I think when I did my first attempt I thinned the whole thing down too much, it took so long to dry in the first place, it probably never got all the way cured. 

So you just put splashes of toloul onto the surface and let them evaporate?  have you had success removing small amounts of bubbles with this as well?

You have to “pop” the small bubbles enough for the toluene to reach them when you splash it.  But yeah, the small surface bubbles disappeared after a few washes, the deeper ones require a little fiddling with, but they go just as easy.  Feel free to lightly scrape or poke the surface immediately after a wash to fix surface defects, because it all comes out in the next wash.

Sorry I keep asking questions, I should have thought of it more carefully and been more concise in my questions.

Do you wash small areas by themsevles, or do you have to do the whole surface in one go?  How long to you let it dry/evaporate?

Hi,

I finally got my new computer, im so happy

I have made another video of my setup with better image quality this time.... 
I have tried to show close up of my screen to show the image quality.
Im quite sure that theres a big difference between my computers now.....

thomas.hansen: For me i had to vigourously wash with a clothe in order to get my acrilic complety transparent again…

Thanx
Christopher

awesome !! ....
gr8 efforts dude ......

well, i am fiddling with the Cheap Rubber Solution past 3-4 days .... gave 3 tries and still something goes wrong .... the layer aint coming even .... i have PMed u (Christopher) din receive ur reply yet .....
can u plz spare a little time ... i need to talk to u .... plz !

At the first, Thank you Christopher to suggest the good way solution. But the material It hard to find in my country. I chage something but still used the main idea from you. I used silicone sealant and mix with thinner. My result It’s great, And then I mixed your solution with Non-Woven form this topic “http://nuigroup.com/forums/viewthread/1217/”. I think It’s not “zero force” but near “zero force”. I glad with this result. Thank you for all solution.

But Experiment is experiment. I had decied to use baby powder to reduce sticky. Form post of Adam

Adam - 14 March 2008 07:05 PM

I have heard baby powder (talcum) or trace paper works.  I am excited. I plan on trying the cheap caulk tomorrow.

Adam, From my experiment that I used baby powder, It made me cry because “BLOB” had gone away from my screen. I didn’t know why it disappeared. But It’s not work for me.

Hi,

Mj:  Im sorry it doesnt works for you! I wonder wich method of application do you use? Can you explain more about the non-evenness of your rubber..I have read your message in a hurry but forgot to answer when i came back… :( I dont use lot of pm… I’ll will pm you with the best I know, I hope I’ll be able to solve your problem…

Hull: Im glad it works for you too.... There’s a lot of combinaison that could be made, the only important thing is to use the same solvent as product made of… I think everyone should post there working combinaison and in wich country they are cause I think it could help several people finding the right product… I received a lot of messages of people trying to find same product as mine in there home country but it may be really difficult so if we make a database of it, people would have an easy solution......

Thanx
Chris

NO ... its not tht it aint working ... am getting gr8 FTIR effect.... just tht the layer isnt coming out to be even.... ill post a few pics later .... wen i get an even layer .... wud be giving a fourth try tomorrow ..... with ma fingers crossed

Are you using a rails and a bar to scrape over your liquid rubber?  Thats what I did to get it even; it also got rid of some leftover bubbles.  Also I have been having success with Adams method of fixing the layer afterwards using splashes of toloune.

ya ... for the first time… i used the same method ... as seen in blaxon’s video ...
then i used wooden bars alongside the acrylic .....
i knw where i go wrong ... still am doing the same mistake ....
the thing dries quickly .. and wen u move the strip wen it gets a bit dry .... it gets crappier ... and then u have to peel off the layer .. and try it again .....

What silicone/thinner are you using.  My rubber took 24 hours to dry.  it didn’t even start getting sticky until about 3-4 hours into drying.  You can see how much i thinned it in the video i posted above.  Its working really great.  I’ll upload some pictures in a while.  When I get it all setup in the lab I will take some video as well.