Running Foam Latex - A Basic Approach
By Gilles Paillet
- The basic components
- Health and safety for you and the environment
- Shelf life and storage
- Pigments & colours for foam latex
- Things you need if you want to run foam latex
- Different ways to fill your moulds (brush or injection)
- Your first run of foam latex
- Working time and gelling time
- Baking your foam
- How to make sure the foam is properly baked?
- How to demould your piece
- Main troubles you may encounter and solution
- Things to do before you can use your foam latex piece
- How to colour your foam latex piece
- Apply your foam latex piece
- Tricks & tips
A kit of Monster Makers Foam or Creature Foam usually is composed of:
High solid latex foam base
Creamed latex, different from prevulcanised liquid latex. White-ish colour, slightly thick, with a strong smell of ammonia. It is the main component of foam latex.
Thick and viscous liquid mainly composed of castor oil (soap) and water. That will help
your foam to reach the volume you want when whisked.The amount of foaming agent to add to your batch/mix is 20% of the amount of the latex base.
Yellow-ish liquid, sulfur-based. It gives your foam its memory (the foam comes back to shape when pressed) and elasticity.
The amount of curing agent to add to your batch/mix is 10% of the amount of the latex base.
Grey liquid. It helps set the batch of foam. The foam goes from a ‘shaving foam’ state to a ‘compact’, ‘solid’ state, prior to be put in the oven.
The amount of gelling agent depends on different factors: temperature, humidity, the refining time… It could vary between 10 and 14 % of the amount of latex base, but could be less if the room temperature is higher than 20°C, more if the room temperature is lower than 20°C.
Release Agent – Mould-release – Zinc Stearate
Pearly foam brushed over plaster moulds, positive mould AND negative mould (or on any porous material) every time prior to casting foam. Temporarily seals the porous surface of the mould. Leaves a residue (white powder) on the mould that needs to be dusted off.
As you are going to manipulate chemicals, it is especially important that you follow a few rules and use common sense:
- Always wear gloves (disposable latex, vinyl or nitrile gloves for example) and a respirator (one with AB1P2-type cartridges is a must as it can be used when manipulating other chemicals). Dust-masks are not efficient enough. Goggles could be considered as well.
- Do not drink, eat or smoke where you run foam. (remember, at the end of the day, you are using chemicals).
- Dress appropriately, wear clothes and footwear dedicated to working in a workshop only, or wear protection suit. Any foam on contact with fabric will stick to it definitively and most likely ruin it.
- Work in a well-ventilated area (with a good air extraction), but avoid working outside, or draughts. Any drop or brutal change of temperature while whisking it may ruin your foam.
- Avoid contact with skin and eyes. In case of projection in your eye, wash thoroughly under running water, for a few minutes, without touching it. After that, if you still feel uncomfortable, consult your GP and tell him what products you have been manipulating.
- To get rid or dispose of foam leftovers, it is best to do so with set foam, rather than liquid components. Dispose of it in a place where they accept chemicals products/residues. Do not throw them in the sink, even on their liquid state, as they could solidify over time and block the pipes.
SHELF LIFE AND STORAGE
The latex base, because of the amount of ammonia it contents to keep it liquid, is the component that will go off first. Ammonia, even if the plastic container of base latex it comes in is properly sealed, will evaporate. You end up with a thick mass of rubber over time. Once the container is open, the shelf life for the latex base is roughly 6 months, a year at best.
The other chemicals, on the contrary, are relatively stable in time, and could be still used more than 6 months after first being used.
In order to keep your foam latex kit usable as long as possible, it is best to shake thoroughly for a few seconds each and every container (no need to shake the mould-release though), every couple of weeks, to avoid the different products to separate and settle at the bottom of the container. It is particularly true for the curing agent: the sulfur it contains could settle and set in a big blob at the bottom of the container.
All the components of your foam latex kit must be kept away from sunlight and freezing temperature.
Keep your products in a dry place, off the ground if possible. If you cannot, isolate them from the ground by using a piece of cardboard, a wood board, etc...
Try to avoid ordering foam latex kits in winter, or when the temperature is low. In short, before November, and after March. The main reason is that foam latex kits are ruined if frozen. You do not know how the products are stored or for how long. And they could be kept in cold warehouses or custom buildings (if ordered abroad).
There are numerous products you can use to colour foam latex or latex intrinsically:
Special latex pigments and colours (made specifically for latex and foam latex), very concentrated colours.
The cheapest ones you can get are food colouring liquids or powders. But food colouring liquid could be not very strongly pigmented, requiring to use a lot of it, adding water to the batch/mix. Powder might prove difficult to disperse properly and efficiently.
Acrylic paints work well but be aware that some pigments (such as red) could contain non friendly foam latex components. Liquitex acrylic paint is safe to use, as it already contains a bit of latex in it to make the paint a little bit elastic. Any acrylic paint with the ACME label/certificate on them is safe to use on skin too (when you paint over them and try to match the skin colour). Always do a test first.
Do not go crazy when adding colour/pigments to your mix. It’s best you add no more than 10 % of the amount of latex base (or you might change the properties of the final product, elasticity, etc.). You can either add the pigment at the beginning of your run, or when you pour the gelling agent into your batch/mix. Again, powder pigments might not work well if you choose to mix it with the gelling agent. Adding the colour to the gelling agent allows you to visualise how well pigments (and therefore, gelling agent) is mixed in your batch/mix of foam (streaks of uncoloured foam: gelling agent and pigments unevenly distributed; Same, even colours : gelling agent and pigments well distributed).
Gouache paints and oil paints are not compatible with foam latex or latex, as they contain elements that work again foam latex components (copper for example), or paint thinners.
- Electronic scale, precise to the gram
- Multiple-speed Mixer with whisk attachment and a big bowl
- Oven dedicated for the baking of foam latex (do not use the one in the kitchen, the products you use are toxic)
- Thermometer and hygrometer
- Notepad (or worksheet) & pen
- Disposable cups (for the gelling agent)
- Gloves, respirator, goggles, paper suit / overalls etc.
- Cheap disposable brushes (One-inch, Two-inch brushes), and/or injection gun (big syringe)
There are 2 basic ways to fill up a mould, depending on the quantity of foam you need to run, the facility and working space you have at your disposal, and if the mould has been prepped or not for injection.
Manually: Mould is laying open, foam is brushed in. It works for small to medium-size moulds, or when you do not have time to install an injection tube. You brush in a thin layer of foam at first, to capture all the details in the negative mould, and then, without trapping air pockets, add more foam on top of it. Until you fill up the mould. Close the mould bu pressing the core or the positive mould onto the one filled with foam and allow the extra foam to overflow. Keep the pressure and the pieces together while someone help you bolt the mould up (fiberglass mould for example) or use gaffer tape to tighten the 2 parts together, large elastic bands, or clamps.
By injection: With an injection syringe (also called injection gun), you inject foam into a closed mould, until the foam comes out by the bleeder holes or through the flashing, or both. You can ask someone to help you plug the bleeder holes once they ‘bleed’ so you don’t waste too much foam.
Another way of doing it is to use both methods described, if the mould is really big or you can’t run all the foam you need at once (limited numbers of mixers available): You start by brushing in the foam (first a thin layer to get all the details, then building up a thicker layer), let it set, and part bake it (say for an hour). If you need to add more layer, do it again, and part bake each layer, and eventually, put the mould back together and inject the rest of the foam. Again, let it set, and bake it. Use a lower temperature for the oven, for a longer period, so the outer skin you have already baked out several times is not so overcooked.
Before you start your mix, make sure you have everything you need. It is very important that you take and keep as many notes as you can, so if you have to do the same piece again, you will use/adapt you notes to run your foam. It is best to use a worksheet (you can use the one provided as such or use it as a template), but a notepad will do. For example, you need to write down:
- Name of the project
- Brand and/or the number of the mixer(s) you use
- Brand of foam latex kit you use
- Room temperature
- Humidity level of the room
- Quantity of latex base you use in your batch/mix
- Quantity of foaming agent (20% of the amount of latex base used)
- Quantity of curing agent (10% of the amount of latex base used)
- Quantity of gelling agent (depending on the temperature, the humidity, etc., always varies but is calculated according to the amount of base latex)
- Time needed for the foam to rise to the volume /aspect desired (fast speed)
- Time needed to refine your batch/mix (slow speed)
- Final aspect of the foam (light, noticeably light, compact, etc.) - the lighter the piece, the better for a prosthetic
- Result once the piece is demoulded
- And whatever annotation you feel is important for the next run
Again, take as many notes as possible, and keep them if you need to change something in your batch/mix. It is basically a matter of trials and error, and you may need to adapt, increase amounts or time, reduce amounts or time, etc. The things that never vary are the amount of foaming agent (20%) and the amount of curing agent (10%).
Keep in mind that the more you whisk your batch/mix, the more ammonia comes out of it and the quicker your batch/mix will gel (set).
Also, the warmer the temperature of the room/day, the less gelling agent you will need.
So, choose the amount of gelling agent you are using accordingly.
After a while, your notes will allow you to determine what you need to do in order to run your foam.
The size of your batch/mix depends on how many moulds you will have to fill up. A zombie half mask (cheekbones and forehead) could take less than 200 grams of latex base, whereas a full head mask of, say, a werewolf could take up to 1000 grams of latex base if the thickness of the mask is important. To know roughly how much foam you need, keep the material you used to sculpt your prosthetic. Place it in a plastic bag and place it in the bowl of your mixer. The level reached by the material of sculpture will give you roughly the volume you are looking for once your batch/mix is whisked. Keep in mind that the amount of latex base (plus all the components) is not the volume. When you whisk it, your batch/mix size is multiplied by between 3 and 4 or more. So, a 200 grams batch/mix give a volume of 600 to 800 grams or more.
Make sure that everything you need is ready (brushes, clamps, clay, cordless drill, bolts and nuts, gaffer tape, etc.), and people are available to jump in to help you if/or when needed. You will not have time to waste when the gelling agent is added to your batch/mix.
Use the mould-release provided with your kit on your moulds. Brush in a thin layer everywhere (negative and positive mould, inside and out), and wait a couple of minutes for the mould-release turns into dust that needs to be dusted off. Keep the same brush exclusively for applying the release agent, NOT for applying the foam.
If you use an injection gun, make sure it is clean and ready to go.
Weigh everything you need in the bowl of your mixer placed on the scale: Latex base, then foaming agent (20%), curing agent (10%), add the colours you need at that point if you choose to. You need also to weigh the gelling agent in a cup separately and set it aside. Allow 1 extra gram which stays in the cup.
Place the bowl back on your mixer and start whisking it at high speed, to give it its desired volume. Start the stopwatch at the same time. Depending on the size of your mix, the temperature, etc., it could take between 3 and 6 minutes or more for the foam to rise up to the desired volume.
Once you have the volume of foam you want, comes the refining time of your batch/mix. Without stopping the stopwatch, turn your mixer’s speed down to the slower setting. Refining the foam means breaking down the big air bubbles in the batch/mix into tiny, smaller air bubbles. Depending on the size of the mix, it could take 5 to 20 minutes or more to get a smooth aspect (no big air bubbles visible). Do not forget to write down every step of the process.
Keep in mind that the more time your batch/mix takes to rise to the volume you want, and to refine, the more ammonia comes out of it, which, in term, will make it gel (set) faster.
Once you are satisfied with the aspect of your foam (that looks roughly like shaving foam, the foam making a ‘Donut’ shape on the surface of the mix (the whisk being in the center), when the whisk passes through), you are ready to add the gelling agent to your mix. Check your stopwatch, and without changing your mixer’s speed (minimum speed), pour the gelling agent gently, distributing it in the batch/mix over a period of 30 seconds, within the space between the outside of the whisk and the side of the bowl. Avoid the inside of the whisk, as foam tends to be not well mixed there. (With a bigger whish/mixer, you can use ping pong balls to move the foam inside the whisk). Use a spatula to scrap the inside of the bowl and bring it in the middle, so the gelling agent does not stay on the side but is well mixed within the foam.
Leave the mixer go for an extra 1 minute and 30 seconds once you have poured the gelling agent in, at the same speed (minimum speed). After that, stop the mixer, take the bowl out of its slot. Let the stopwatch run. And it is time to fill up your moulds.
At this point, you have a few minutes minutes to either:
Brush the foam in, a thin layer at first, to catch all the details inside your mould. Build up with thicker layers (you can gently tap your mould against your workbench to pop up trapped air bubbles in the foam) until you fill the mould up. Put the mould parts together and bolt them up or use some gaffer tape, large elastic bands or clamps if you are using plaster moulds. The excess of foam will be pushed from the inside out. If you are using plaster moulds, place the positive mould in the negative mould (face or positive mould facing down).
Fill up the syringe, (plunger pulled back completely, tip removed for easy access) held at a 45-50 ° angle while being filled. Put the tip back on, push the plunger slightly so the foam starts to come out from the tip/nozzle. Start injecting the foam by pressing gently and regularly on the plunger, allowing the foam to flow everywhere in the mould. When the foam comes out of the mould by the bleeder holes, plug them with water-based clay. Then plug the injection tube.
Once your mould is filled with foam, let the foam gel (set) completely before you put it in the oven (no trace of ‘liquid’ foam).
After 20 to 30 minutes, check the state of the foam leftovers or overflows to see if the foam goes from ‘foamy’ to ‘solid’ to the touch. Poke the leftovers: if you feel there is still liquid foam under a skin of solid foam, when pressed, that means it needs more time for it to gel. If you press and leave a fingerprint or a mark on the foam, it is likely to be ready for the oven. If the foam is still not set after 1 hour, this is likely that you need to adjust either the refining time, or the gelling agent amount for the next run of foam. Once the foam is thoroughly gelled (or set), it is time to bake out the foam.
The oven’s temperature is 85-89°C, and the thicker part of the mould determines roughly the time it needs to stay in the oven: If the mould is made of plaster, it takes 1hour of baking time per centimeter (Half an inch) of thickness of the mould. Same with polyurethane resin moulds or jacket silicone mould.
If the mould is made of fiberglass (polyester or epoxy resin), it takes roughly an hour of baking time per millimeter of thickness of the mould.
Try not to bang the mould while putting it in the oven, as it might dislodge the foam inside the mould.
The foam must be baked for a few hours, depending how thick and what material your mould is made of, and the amount of foam there is. Make sure your oven is in a well-ventilated area or has a good extraction, as the smell of baking foam is quite stinky.
If the piece you need to do is big and you had to do several mixes to get it all filled, you will need to partly bake (for about 1 hour) each layer before you add a new one on top of it. If you can’t use your oven overnight (with a timer), you can either leave the mould out of the oven and bake it the next day, but if you decide to part bake it, leave it at least half an hour and turn the oven off. And then finish to bake it the next day for the time remaining.
If your foam, after baking, looks grey-ish or brown-ish, it means it is overcooked. Meaning that the characteristics of the foam have changed, and the foam is slightly weaker. Steam the piece to get rid of the grey-ish or brown-ish colour. But it will be less stretchy, the foam losing its properties.
To make sure the foam is properly baked, poke a bit of leftover foam or overflows (on the outside of the mould for example). If the foam springs back, the foam is likely to be cooked. If it does not, put it back in the oven and check it out every half hour until you are satisfied that the foam is baked.
If your mould is made from plaster, or any mineral material, you cannot take it out of the oven straight away. The thermal shock (temperature difference between the inside of the oven and room temperature) would most definitely crack it and most likely damage it badly. In order to avoid that, turn the oven off, and let it cool down for an hour or at least until the oven temperature is close to room temperature before you take your mould out of the oven.
If your mould is made from resin/fiberglass, no thermal shock to dread, you can take it out straight away without risking any damage to it. Wear proper gloves though, as the mould is hot.
In order to demould your piece, you must be careful. In porous moulds, the foam might still grab the material of the mould a little, but for a resin mould, it is easy. However, use baby powder and a small brush to ease the process, as you go along, like you would do with any latex piece. Be especially careful around thin edges. Powder the entire surface of your piece, so it does not stick to itself.
The foam looks very stringy, only has a thin skin, instead of filling up the mould.
The foam may not have been completely gelled (set) prior to start baking.
You need to start the process over. But this time, make sure the foam is completely gelled (set) everywhere before you put your mould in the oven. Check in several places to make sure. Give it another 15-20 minutes even if you think it’s gelled properly.
The foam does not fill the mould completely and seems to have collapsed in places (especially in fiberglass moulds).
One or several steam pockets have formed during the baking, pushing against the foam, leaving a gap between the side of the mould and the foam.
- Make sure the foam is completely gelled (set) everywhere. Check several points to make sure. Give it another 15 minutes or so, even if you think it’s gelled properly before you put in the oven.
- Drill more bleeder holes. You can also reduce the temperature of the oven (baking the mould for a while longer).
- It helps to spray a layer of permanent spray glue on the negative mould before you brush the foam in or inject it.
The foam has a grey-ish or brown-ish aspect to it.
The foam is overcooked.
Steam the piece to get rid of the overcooked colour. The foam remains slightly weaker.
When poked, the foam does not spring back.
The foam is not completely baked.
The foam needs to be baked for a longer period. Check every half-hour.
Once you have demoulded your foam piece, you cannot use it straight away on someone’s skin. It still is full of nasty chemicals. You need to wash you foam, in several baths of warm soapy water, until the water remains somewhat clear. Then rinse it thoroughly (a couple of baths, with just warm water, no soap). The foam piece needs to be squeezed to get rid of the water (either in a mangler or between a couple of towels. Let the foam piece to dry gently, flat, or better yet, on a form similar to the positive mould used to get the foam piece.
Once you have applied you foam piece, and before you can colour it, you need to seal the surface of it, otherwise the colour will sink into the foam unevenly. Use pros-aide (or PAX – Pros-aide and acrylic paint) to seal your piece. Powder it. Now you are ready to use different method/colours, or a mix of it:
RMGP Palettes (Rubber Mask Grease Paint) Special Latex Paint
Opaque colours, grease paint. Use powder to set the colour. Build up layers of colours to make it more natural. It needs to be powdered to set the paint properly.
Alcohol Activated Colours
Translucent colours, applied most of the time in a spritz manner, with a short/cut bristle brush. Avoid applying around the eyes.
Mix of acrylic paint and Pros-aide (usually 50/50, but you can change the ratio if you want it thicker or runnier). Same way to use than with the RMGP. Only a little more resistant to stretching and rubbing. Liquitex acrylic paint is best to use to do PAX paint. Using PAX paint keeps you from sealing the foam surface first, as it does it at the same time as colouring your foam. Use transluscent powder to set each layer.
Airbrush and Airbrush Inks
Can be used in conjunction of makeup. Use acrylic paint or especially designed coloured inks.
Rubber Cement and Thinners
Toxic sealer/paint used with thinners such as toluene. Make sure you wear proper protection as it is very nasty and work in a very well-ventilated area.
Apply your foam piece using pros-aide, or the like, one bit at the time. You can pre-paint your piece prior to applying or paint it using colours as said before. Before applying any colour on it, the surface of the piece needs to be sealed, so the colour apply on top of it does not sink unevenly but stay on the surface of it. Apply a thin layer of pros-aide or the like to seal your piece. Or Pax paint, which allow you to apply a first colour to your piece as well. Then powder it
Each prosthetic can only be used once: Using the remover (Supersolv for example) destroys the thin edges of your foam.
Each foam piece is made to order and is meant to be used rapidly. In case you need to make several copies, you can store them in a sealed box (preferably, but not mandatory) but away from sunlight.
Removing a piece or a makeup properly is particularly important. Take your time. Bond-Off or Supersolv are good removers. Use sweet almond oil around the eyes. Keep in mind to be as gentle as possible to the model’s skin. Never rush or pull a glued piece off. Let the remover dissolve the glue.
Use soapy water to clean the whisk
Once your mix is ready to be poured/injected/used, you can wash quickly your whisk in soapy water, or you can leave the foam on it to set, and snip it to free the whisk. The latter way takes time though.
Use permanent spray glue to get the foam to hook on to the mould
In non-porous material used to make a mould, foam does not stick well to the side of the mould and often results in skrinkage or ‘steam-collapse’ of the foam. Use permanent spray glue to make the foam hook on temporarily to the inside of the mould. The glue will not remain in the mould or on the foam piece.
Never use copper metal
It makes the foam go black (stain due to chemical reaction).
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