How can a make very thin layers of silicone?

Fred Kemp

I am making a medical surgery model our of various silicones and am making good progress.  Cosmetically, the Winston tutorials have helped a lot.

However, it seems that most organs have a thin membrane around them with thin veining within them.  And, any surgical procedure involves removing this membrane (including the kitchen scene with Hannibal Lector taking the membrane off the brain of the guy with the top of his head cut off) 

The membranes seem to encapsulate whatever they are around, but are attached weakly or not at all.  So, it would seem that I would have some kind of release on the base organ and maybe applying silicone is some way in a very thin layer.  Then, of course, I could air brush the veining.

Any help on how to make these membranes would be greatly appreciated! 

Thanks.

Chris Ellerby

One option would be to put a release on the target subject and then airbrush silicone in thin layers.  You could brush on a couple thin layers, embed threads/veins as needed or paint on veins, and finally airbrush on your final layers.  For the airbrushing I would suggest an external mix airbrush like the "Paasche H."  It's inexpensive and very easy to clean.  It's my go-to workhorse airbrush for stuff that would be impossible to clean out of my more expensive iWatas.

Depending on the nature of the membrane you could also try airbrushing bald cap plastic like Super Baldiez, which is a solvent based polyurethane.  This material is often used to encapsulate silicone appliances.

If a membrane material in sheet form would suit any of your needs, "dental dam" is frequently used in the effects world for membranes. 

Another option might be cellophane.

/Chris

Fred Kemp

Thanks Chris for the pointers . . . I'm going to experiment with your suggestions right away.

But, I do have a few questions for you, if you would . . . 

Do you recommend the single-action Paasche H for ease in cleaning or to spray more material to make the silicone layers?  Also, which nozzles would you use?

Since the Super Baldiez is a polyurethane, would you need a release with silicone?

On a separate but related point, the inside of the human body is, of course, wet with body fluids.  So, I suspect an oil might be best to simulate the wet look over time.  If that is the case, could an oil be the ideal way to both act as a release in painting additional membrane layers (in any material) and providing a continuous wet look?  What would you recommend?

Thanks again!

Fred

Chris Ellerby

The single-action Paasche H is great for a lot of reasons, ease of cleaning being one of them.  When it's easy to clean you can spray more messy/viscous materials (like cap plastic or thinned silicone) without worrying.  With silicone you would still need to thin it down with something like Naphtha to make it sprayable.  You want a consistency similar to that of milk to get good even coverage.   Most of their nozzles should work, as you can open them pretty wide, but I would go with a medium/large nozzle.

It's also a very low-cost airbrush, so you don't have to worry about replacing it should the testing of a new material not work out as desired. 

It is also great for painting small spatter/freckle patterns when operating at low pressure with the tip wide open.

If you are spraying a plastic membrane like Super Baldiez or something like a vinyl cap plastic on silicone you would only want to release the silicone if you want that membrane to appear free-floating or be easily separated in the final effect. Without a release they will lightly bond with the silicone, but should still peal up easily.  You'll want multiple coats (possibly 5+) to get a thickness of cap plastic that will not easily tear.  But that all depends on the effect you are going for.  You can try different materials, and different numbers of coats to see how the materials react in your particular application.

For a release agent you could either lightly brush on vaseline or use a release spray.

Also keep in mind that you would need to repeat this process to replace the membrane every time it is cut or damaged during use.  So you may want to have a duplicate of each surface that will have a membrane and use that surface to spray silicone membranes on that you could then carefully remove and stretch over the working model.  That way you can have plenty of replacements.

If you are spraying a silicone membrane onto a silicone surface you will need a thorough release, as silicone sticks to silicone

For the wet look there are plenty of options.  Glycerine is a common one.  The most common is probably KY (or other water-based lubricants), as they give you a good wet/slimly look without being too thick, and can easily be thinned/re-activated/washed off with just water.

If you want something more thick and stringy like mucus, you can go with "Ultra Slime" (a brand of slime you can get off the shelf) or if you want to make it yourself you can use Poly Lube or J-Lube.  They are a polyethylene polymer lubricant often used in livestock birthing.  They come as a dry powder that you add to water.   One great thing about going that route is you can tailor the thickness of the slime to your application by adding more or less powder.

I would go the water based route over oil, as oils are more difficult to clean up, and can get rather messy when transferred to other surfaces.

Silicone pieces can often look wet and shiny even when dry if the surface is smooth.  People often fight that shine with dulling spray or by dusting their mold with baby powder before casting, so you can use that natural shine to your advantage.  You may even be able to get by just misting water onto the surface.

/Chris

Fred Kemp

Chris,

All great information, thank you!  It did not occur to me to make membranes other than in place . . . 

Sounds like the H Model is the way to go . . . 

Membranes with a slight adhesion that could be easily separated would be ideal.

I've got some Super Baldiez on the way . . . 

If I use KY, what would you suggest for coloring?

Thanks.

Fred

Chris Ellerby

You could use quite a few different pigments.  (food coloring, acrylic ink, acrylic paint, anything water soluble)  One good option for red would be Ben Nye's blood powder, which comes as a dry powder that you can add to any liquid you wish to pigment.

But if the color you want is that of blood, you could just as easily go with any number of off-the-shelf bloods.  Ben Nye makes some ok quality blood that is easy to find and rather inexpensive.  I often use a brand called "My Blood" which has a good selection of color variations.  Fleet St. is also a great blood brand, but they are a bit more expensive.  (but you get what you pay for)  And I'm sure a lot of the other folks on here can chime in with their favorite blood brands/recipes.  

You can also make your own blood.  Here is a basic recipe:

• Water as a base 
• Karo syrup as a thickener 
• Red food coloring
• Green food coloring to darken the red  (green darkens without changing the red value too much, blue will push it towards purple, yellow will push it towards orange)
• Drop or two of dish detergent to help discourage staining.

Start with the Karo in a large container, and add water until you reach the desired thickness for your application.  Then add the red food coloring until the color looks right.  Test the color density by spreading a small bit out on something like a paper plate.  The blood will look much lighter when in a thin pool/smear than in your main container.  Then add green a drop at a time until the desired shade is reached.

As your application is medical, you may want different colors for different types of blood (oxygenated vs non-oxygenated, pooling/clotting blood, etc.)

I would also be careful when experimenting with pigmenting KY or any blood mixture and test to see how easily it can be cleaned from the surfaces/materials involved in your project. 

/Chris

Fred Kemp

Chris,

     Sorry it took me so long to get back to you. Had to meet a deadline.

     Thanks again for the information.

     Do you think I could replace Karo syrup with KY Jelly (I'm trying to keep a water base)?

     Thanks.

Fred

     

Chris Ellerby

You can use KY as a thickener as well, it's just a bit more expensive and has slightly different properties than Karo syrup.  I would suggest finding a generic store brand of equivalent water-based lubricant if you want to go the quick off-the-shelf route.

But if you want any quantity, I would suggest going with Methyl Cellulose powder (which is the main ingredient in KY).  It will create a good thick/clear liquid that is not stringy like the polyethylene polymer lubricant.  And when you mix your own, you have more control over the consistency.

Methyl Cellulose is used a lot in effects, one classic use is the slime that drips from the mouth of the Xenomorph in the Alien movies.

You can also use the polyethylene polymer lubricant In a thinner mixture (lots of water to very little powder).  As you add more powder they get more stringy/mucus like.

/Chris

Fred Kemp

Great.  We need to be able to pump the blood somewhat continuously and I think Karo would eventually gum up the works.

Thanks again.

Fred

Chris Ellerby

Depending on how you plan on pumping it you may want the mixture to be pretty thin.  Some manufacturers of special effects blood sell blood designed for pumping, which has a lower viscosity.

Best of luck!  And I hope you can share photos/video of your creation when it's ready.

/Chris

Fred Kemp

Thanks for all the help!

Chris Ellerby

Any time!

/Chris