(Editors note: This article was originally written by Tom McLaughlin for the American Anaplastology Association Conference in Washington DC in May of 2000. Tom has kindly allowed me to reprint this paper which I consider to be a wonderful introduction to using silicone GFAs.)

Solid Silicone Appliances are of great importance in the medical prosthesis field as they are very durable and can last a patient 5 years or more. Solid silicone appliances are usually made from medium-firm silicone (shore A-30 - A-40) and what they lack in subtlety of movement they make up for in durability. Solid silicone prosthetics may be use hundreds of times. Limbs, hands, bald caps, head pieces, masks prosthetic nose tips, chins, ears and of course molds can all be made in solid silicone.
Silicone Gel Filled Appliances (GFAs) are used where realistic movement is important for motion picture makeup and for patients that can afford the added expense. Unlike foamed latex, traditionally used in makeup, which being a sponge collapses into its self when moved, silicone gel filled appliances displace themselves, remarkably like real tissue. Existing molds may be utilized and it is hoped that after supplying a patient with durable solid elastomer appliances, that you may take the time to experiment with silicone gel filled technology. Movement considerations aside, feeling the flesh like texture of a silicone GFA may do wonders to boost a patients confidence, emotional and psychological well being. At the outset, GFAs may be added to a patients collection for special occasions. Once the technique is learned and perfected, silicone GFAs may become the norm in many applications.
A development from silicone breast technology, Silicone GFAs incorporate a tough elastomer encapsulator over soft silicone gel that approximates the qualities of human skin over soft fleshy tissue. Silicone may be manipulated over an extremely wide range consistencies, from a firm 80 Shore A (like tough sneaker soles), to rubbery 30 Shore A, down to gels measured on the Shore 00 and 000 scales. Platinum silicone gels hold their shapes better than most other rubbers.
The encapsulator skin may be made of silicone, urethane or acrylic. There is a chemical bond between silicone encapsulator and silicone gel but not with the other encapsulators For ease of use and compatibility, silicone encapsulator and gel are recommended for beginners.
MATERIALS Many individuals and organizations have been 'pushing the envelope' with this technology, and a wide range of materials has proven useful for manufacturing Silicone GFAs on a small scale. These materials are all stocked by FACTOR II and are available in conveniently sized packaging. Inexpensive starter kits are available to experiment with.
The SILICONE ENCAPSULATOR of choice is TS-401 (6600) for its unrivaled ability to help block silicone fluid migration from silicone gel- the main cause in silicone adhesive failure. TS-401 is a transparent 2-part medical grade heat cue platinum diphenyl silicone dispersion mixed 1:1. 1,1,1 Trichloethane, Naphtha or Stoddard Solvent may be used to thin the material down for spraying or brushing onto mold sections. It will form weak film at room temperature, although full physical properties will not be attained until heat is applied. Recommended cure schedule is 2-3 hours at 200 F. TS-401 Physical Properties: Tensile Strength 900 psi, Tear Strength 90 ppi (Die B) and Elongation of 700%
The most popular silicone Gel is A-208 (527) a transparent 2-part RTV platinum silicone gel. Originally designed as an electronics potting compound, this clean gel is rapidly becoming the standard for Platinum Silicone GFAs in Hollywood Effects shops. Aside from its lower price, the beauty of using this material is that the recommended 1:1 ratio may be varied by the user to produce firmer gels. 80 parts A to 100 parts B is a popular consistency. (For the adventurous- a small amount of uncatalyzed silicone elastomer such as MDX4-4210 or A-588 may be added to a 1:1 mix of A-208 to make a firmer gel.) A-208 is Room Temperature Vulcanizable and demoldable in 24 hours. Being a platinum silicone it may also have its cure accelerated by heat -4 hours at 150 F/ 65 C, 1 hour at 212 F / 100 C.
Another useful gel is A-827, a 10:1 platinum silicone gel that is a bit 'meatier' then A-208.
A common misconception regarding silicone gel filled facial appliances is the consistency of the gel. The most successful appliances are made with a gel much firmer then you would find in breast implants and breast enhancers. There is room for development of gel materials with a consistency between existing gels and very soft rubbers.
ADHESION is ever so important to bear in mind when constructing appliances intended to be temporarily glued to the skin. Many silicones may be used to make breathtakingly realistic appliances, but if you cannot adhere them to a performer or patient, they are of little use. Silicone Pressure Sensitive Adhesives such as Hollister, Telesis and Secure Medical Adhesives are all based upon partially cured silicone gum and, because they are partially cured never loose their tackiness. The slightest amount of silicone fluids migrating from solid silicone elastomer or silicone gel through an encapsulator will rapidly turn the adhesive to goo, and render the adhesive useless. This is why TS-401 is such a valuable material. You may have had personal experiences with Silicone pressure Sensitive Adhesives failing to effectively adhere silicone appliances. TS-401 may also be used as an adhesion promoter with problematic solid silicone prosthetics- either painted into the positive mold before casting the elastomer, or painted directly onto the rear of once a silicone appliance has been demolded, then cured.
Blending Edges (margins) One of the main differences between medical and theatrical appliances is the fine edges demanded in motion picture work. For imperceptible blending into surrounding skin, a tissue-thin 'feathered' edge of encapsulator material is created when first applied to the mold sections, usually by airbrush. 4-6 lightly sprayed coats of encapsulator (thinned 50/50 with appropriate solvent) on both negative and positive is usually sufficient for motion picture work. Carefully manufactured, applied and removed Silicone GFAs intended for closeup film, television and live work may be reused several times, up to 5 or more applications, maybe 10 if you are meticulous. Traditional makeup appliance materials such as latex foam and gelatin are used once and then thrown away due to delicate edges being ruined during removal.
For medical applications, slightly thicker encapsulator (and edges) will give more durable silicone gel filled appliances that may withstand upwards of 50 careful applications. Maybe 6-10 coats sprayed as above or 3-5 undiluted brushed coats.
MOLDS Existing gypsum or dental stone molds may be used with this process, with minor modifications depending upon the method used.
One problem you may encounter with molds originally designed for casting thick silicone elastomers in is that silicone gel is runny and may seep out before curing. Cabosil or Aerosil brands of fumed silica may be used to thicken wet gel to prevent running out of the mold, but will have a firming effect on the gel. This firming can be worked into your formulation. Evacuation/de-gassing thickened gel is essential for clarity.
CASTING There are several methods of casting silicone Gel Filled Appliances. We will concern ourselves with two methods here. The first is the easiest, the second produces the finest edges.
HAND FILL METHOD Existing molds may be used without modification.
In pre-released mold sections, paint or spray mixed silicone elastomer material and allow to thoroughly dry. Mix and color gel, de-gas in evacuator or let sit until no air bubbles are visible. Pour gel into negative mold, fit negative mold sections in place, clamp securely and cure both materials in an oven. Recommended cure schedule for 1' thick gypsum molds is 2-3 hours at 200 F. Let mold cool to handing temperature. demold, wash off release and powder.
INJECTION FILL METHOD Molds must be modified for this method to include 2 holes on the positive mold section- one to inject the gel into, the other to let air out as the mold is filled. You will need a polyethylene or polypropylene syringe to inject gel- a syringe without a containing rubber plunger. (Any trace of sulfur will prevent platinum silicone from curing-ever)
In pre-released mold sections (make sure there's release in the two holes) paint or spray mixed silicone encapsulator material and to thoroughly dry. Close and securely clamp mold sections and cure encapsulator material by its self- recommended cure schedule for 1' thick gypsum molds is 2-3 hours at 200 F. Allow mold to cool to handling temperature and remove from oven. Mix and cool gel, degas in evacuator or let sit until no air bubbles are visible. Fill syringe with mixed gel and slowly inject through 1 of the 2 until gel starts coming out of the second hole. Remove syringe, gently tap mold and tilt to work any remaining air through the 2 holes. Reinsert syringe and top if needed. Gel may be allowed to cure at room temperature for 24 hours, or mold may be placed in oven for additional 1-1 1/2 hours at 200 F to cure gel. Let mold cure to handing temperature, demold wash off release, trim injection holes and cover with encapsulator, cure and powder.
APPLYING ENCAPSULATOR Apply encapsulator painted by hand with a brush, or by spraying through an airbrush, Only in well ventilated area, preferably in a purpose made spray booth. Spray with air pressure under 10 psi. If you can afford the 1,1,1 Trichloroethane, this will dry the fastest. Some feel it dries too fast and prefer a slower drying solvent such as naphtha. Thin as appropriate- at least 50/50 for spraying. Certainly do not use Dlimonene as about 5% is non volatile and may impede adhesion (Its great for clean up and as a solvent for painting the artwork side of silicone) Try various brushing directions to avoid wrinkling in the direction of brush strokes. The encapsulator material is surprisingly strong in thin cross-sections.
Fine Blending edges (margins) are a matter of experience, lab technique, and excellent molds. You may want to pre-mark your margins on both positive and negative mold sections for reference. Maybe a faint line of Taupe or Auburn eyebrow pencil, any reference from which may be removed from an appliance with alcohol. You may want to start with a thin layer of encapsulator that goes slightly over the line, with successive layers worked away from the edge. This is how a 'feathered' edge is built up. Again, this is a matter of f personal experience, Do take notes as to how many layers, brushed or sprayed, dilution ratio air pressure etc.
TO TRACE EDGES ONTO MOLD Do a proof in elastomer, alginate or gelatin. Be sure to clamp mold tightly. Demold carefully. Place proof onto each mold section and trace edge onto mold section with eyebrow pencil.
You may find that a combination of techniques to your advantage, such as spraying a fine blending edge and then building up a durable silicone skin on the body of the piece with a brush. Stippling the encapsulator with a brush may give you a more organic wrinkling movement in some applications. Once Several uncolored layers have been applied to the negative mold (artwork section) subsequent layers may be stippled that are lightly tinted with the appropriate colors for effect. TIP: Spray or paint a thin layer of encapsulator over all face surfaces of both positive and negative molds to aid easy removal. Should any gel flow onto uncoated mold sections demolding can be difficult and messy.
TIP: For EXTRA STRONG MARGINS spray or paint several layers of TS-403 (6640) into your molds before TS-401. TS-403 has greater elongation and tear strength then TS-401, but does not prevent fluid migration. OUT-GASSING can be a problem when using solvent dispersions of silicone, especially in porous gypsum molds. Distortions will appear on the surface of your silicone gel filled casting - indentations where none were sculpted, usually with much of the detail intact. This is caused by solvent evaporating into the pores of the stone while drying and being forced back out while gel and encapsulator are being cured at an elevated temperature. This can be remedied by ensuring solvent has thoroughly evaporated before curing by allowing extra time to air dry, or forcing dry with a hair dryer on cool or warm. 'Ramping up" the cure temperature can also help - starting your cure at a low heat and slowly increasing heat to drive of excess solvent before recommended cure temperature is reached.
COLORATION FOR BEST ADHESION to help ensure no free silicone fluid migrates from your appliances use only dry pigments, flocking or pigments dispersed in functional silicone fluid for coloration. Functional silicone fluid actually becomes part of the elastomer matrix upon curing and does not appreciably effect the softness of the elastomer as non- functional silicone fluid will. Non-Functional silicone fluids bleed and migrate out of an appliance and will give you all sorts of headaches with adhesion. FOR ADDED ADHESION INSURANCE- DO NOT COLOR FIRST FEW LAYERS OF SILICONE ENCAPSULATOR. Besides, the encapsulator's transparency will visually blend better into surrounding skin under a variety of light sources, then if pre-colored.
LAYERING DIFFERENT CONSISTENCIES Shrinkage in silicone is barely measurable and since silicone will bond extremely to its self, different layers of various consistencies may be worked into an appliance. This may be used to simulate different consistencies of tissue, muscle, cartilage, and bone. It may also be employed to allow for magnetic or mechanical fixtures on the rear of the appliance. Or simply to keep a large GFA from collapsing into its self.
A most useful material for firmer portions of silicone appliances is A-588, a semi-translucent platinum RTV silicone with a choice of 3 catalysts giving different cured durometers: soft Shore A-12. Medium Shore A-23, firm Shore A-29. It works well with Thixotropic Additive. The beauty of this system is that no silicone fluid is necessary to make the material softer, manipulation is solely accomplished by controlling the severity of crosslinking. Being a platinum silicone, cure may also be accelerated with heat. A-588 may also be mixed with A-208 Gel for intermediate consistencies. You may also want to experiment with the silicone elastomer you are now using.
TOM'S TIPS AND SUGGESTIONS
FIRMING UP GEL WITH ELASTOMER Mixed 1:1 A-208 is too soft for most applications. While it is possible to make a firmer A-208 gel by reducing the amount of part A, after a while you will find that you have much more part A than part B. To my knowledge, parts A & B are sold together as a 50/50 kit, and are not available separately. You may add a small amount of platinum silicone elastomer to a 50/50 mix of A-208 Gel to make it firmer. For a small increase in firmness DO NOT ADD ANY ELASTOMER CATALYST. For larger increases in firmness add recommended amount of catalyst.
PROOFING MATERIAL To save the time and expense of casting a solid silicone or silicone gel filled appliance to check for fit and finish I recommend gelatin. It will not affect future silicone castings. A 'proof' can be cast and demolded in about an hour at a fraction of the cost of silicone! All you need are the materials, a microwave oven and a mold. Any residue from gelatin may be cleaned from molds with water. (Editors note: in Tom's original paper a photo copied instructional sheet was provided from The Makeup Designatory. I have not received permission to reprint this piece. However I have placed a link here to the wonderful article written by Mitch Boudrot on Using Gelatin for prosthetic makeups on FXMANS page)
DICK SMITHS ADVANCED PROFESSIONAL MAKEUP COURSE may be of interest to you. Dick is considered to be the grandfather of modern prosthetic makeup and this course covers the entire spectrum from molds, to casting foam and silicone, animatronic mechanisms, to makeup. This is a written course of over 700 pages, black and white illustrations, 80 color slides, a video on appliance application, update newsletter, plus Dick's advice by phone. Its sent by mail, all of it for $1995 in thirds for $665 each. It's not for beginners. Some basic experience is necessary. There is no finer work available on modern prosthetic makeup. For info: Dick Smith, 27 Wilford Ave, Bradford, Connecticut 06405.
RESURFACING DAMAGED EDGES Torn and damaged edges may be repaired by placing the appliance back onto the positive mold it was made on, stippling or spraying a new batch of encapsulator over the existing edge and on to the positive, then curing. Curing may be accomplished in an oven or locally, with a heat gun (be careful not to burn the elastomer). Resurfacing appliance edges is a service that the prosthetist can offer patients, effectively extending the working life of a silicone GFA.
MOLD RELEASE FOR SILICONE CASTINGS I've been casting rubbers and plastics for more then 30 years and the fewer toxic materials I need to work with, the better. I like to keep spraying to a minimum as well. Waxy and oily mold releases require solvents for removal from cured and any residue can cause serious silicone paint and adhesive failure. For more then 10 years I have been using DISH WASHING DETERGENT or BABY SHAMPOO as my primary release for silicone from gypsum, plastic and silicone molds. This may not be the release for everyone, you'll want to evaluate it for compatibility with your methodology. The beauty with these materials is that they are cheap, readily available and wash off with water. No toxic solvents are needed for removal. Thin with clean water before application. Apply 2 or 3 light coats, drying between each. TRICK WITH SILICONE FROM SILICONE MOLDS: Water based dish detergent or baby shampoo will ordinarily bead up on silicone molds. The trick I've found is to apply the release with a brush and, while constantly moving brush around mold surfaces, dry with a hair dryer on warm setting. As the detergent dries it thickens, forming a film on the silicone. 2 or 3 coats is usually enough. Be sure to put enough release on the raised portions of the mold.
GETTING HEAT THROUGH STONE MOLDS To my experience, it takes roughly 1 hour for heat to work its way through a 1" thick stone mold. Add this time to cure times quoted by manufacturers to play it safe.
INEXPENSIVE OVENS You may want to look around electrical appliance and department stores for CONVECTION OVENS. Consumer convection ovens are usually about the size of a microwave oven but operate on very different principles. Convection ovens work with radiant heating elements- like your electric kitchen oven. There are lots of them out there that separate prosthetic molds will fit into, if you scout around you may be able to find one that a full face mold will fit in. I picked up mine for less then $200 at an electrical department store and it includes a thermostat, timer, and a fan to circulate the air. The brand is Welbilt and a full face mold will fit easily into it. You may find the heat controls on convection ovens a little lacking, but n inexpensive thermometer will tell you all you need to know about what temperature you are running at.
TEMPORARY TATTOO PAINTS These products are sold in two forms, a fluid meant to be airbrushed, and solid form available in handy 8 color palettes. The solid form is dissolved in 99% alcohol and applied in washes to the skin or prosthesis. More permanent then theatrical or street makeup, Tattoo Paints are quite 'dry'and have no mineral oils that can migrate into a silicone appliance. They are successfully being used to color and touch-up silicone makeup appliances on a performer. Manufactured by Reel Creations (818) 356-7335 as the REEL Fleshtine Pallette and by Premiere Products as Skin Illustrator (800) 346-4774. Not as permanent as painting silicone with silicone paint made from Medical Adhesive A and pigments. Tattoo Paints may prove useful to color an appliance while on a patient (away from the lab if need be) and use it as a model from which to paint other appliances in the lab. While not perfect, these come close to being the ideal temporary silicone 'makeup' and grip silicone better then ordinary cosmetics.
INTRINSIC COLORATION Unlike silicone elastomer appliances Silicone Gel Filled appliances do not lend themselves well to intrinsic coloration, The gel is so runny that even when thixo additive and/or fumed silica are added it is not very manageable, intrinsic coloration may be used on the encapsulator for freckles, liver spots and veins with suitably colored encapsulator material.
1 PART RTV ACETOXY ENCAPSULATOR FOR SEALING INJECTING HOLES Room Temperature Vulcanizing TS-409 may be used to seal the 2 injection holes on the back of Silicone GFAs as made with the INJECTION FILL METHOD with out need to heat cure the piece, Simply cut off the excess, coat with a layer or two of TS-409 and let cure over night. Keep away from molds for platinum silicone work - they are incompatible.
SULFUR WATER WARNING If you didn't already know, platinum silicone will never cure in the presence of sulfur. In 1999 I gave a series of lectures in Orlando, Florida and found that the local water was so high in sulfur you could smell rotten eggs as lawns were watered! This means that any alginate impressions and gypsum stone molds made with Orlando water will render platinum silicone castings useless. Check your local water if in doubt. Use distilled water for safety.

Tom's Favorite Words Of Wisdom
GOOD MOLDS ARE MADE - EXCELLENT MOLDS ARE DESIGNED
Don't Reinvent the Wheel
Do It Right the First Time
Don't Fix it if It Isn't Broken
You can only pick two of the following: GOOD FAST CHEAP
A Feel Is Worth A Thousand Specification Sheets
The Easier it is to make, the easier it is to fix.
ANY FOOL CAN MAKE THINGS MORE COMPLICATED