Last modified by Hypno Harem on 2024/01/07 02:39


The master is the original item a mold is built from.

Masters generally fall into three categories:

  • Life Cast
  • Hand Sculpt
  • 3D Print

There are other methods and even mixes of these methods, such as 3D scanning a life cast to 3D print and resizing later; or adding clay to a life cast and further hand sculpting. Whatever method you use, always test your masters for cure inhibition. This also applies to methods you have used previously until you are vey confident. Paint will not cure fully, or an interaction between monster clay and a sealer will be different than last time, flopping a mold and leaving a hard-to-clean residue on the master.

To test for cure inhibition, mix a very small amount of mold silicone and drizzle it over the master. Allow it to cure and then pull it free. Check the underside of the silicone to make sure it has fully cured. Also check the master for any residue. There will likely be some silicone oil from leaching, but there shouldn't be anything sticky left behind.

Life Casting a Master (This is a stub section, if you can contribute please reach out.)

Life casting involves curing a mold material directly to a person. The mold material can be either a silicone sake to cure against skin such as Body Double or a crystalline-silica-free alginate. Alginates come in fiber-reinforced powders, regular powders, or liquids. You will want to make sure that whatever you use is free of crystalline silica. There is more in Shop Safety, but just be aware that incidental exposure is not the same as continuous occupational exposure to things like airborne silica.

Body Double is a great material for casting anything other than erectile tissues. For that, a fast setting alginate like Alga-Safe Breeze is recommended. Smooth-On has a tutorial on life casting a hand using Alga-Safe Breeze HERE which can be adapted. Whenever casting erectile tissue, be aware that you are applying a cold goo to a sensitive body part. Most people will find that a challenging situation to be in.

Alginate molds are usable, at most, only a few times. This includes the Clone-A-Willy kits. They are not stretchy and resilient like silicone and they degrade quickly, rip easily, and leach water. Alginate molds should be turned upside down to drip out any leached water before being filled, and a quick rinse with alcohol can help dry the inside even more. Since these molds are temporary, it is best to cast a resin or plaster of paris master in them as soon as possible. The master can then be sanded, painted, and finished the same as other masters. Not all resins are good for casting into alginate and not all resins are compatible with silicone, causing cure inhibition of future molds without proper sealing. Plaster of paris masters should be left to completely dry, which may take several days or even weeks. You can oven dry plaster of paris masters, but you should research the heating protocol before doing so as sticking it directly in a preheated oven will destroy the master.

Hand Sculpting (This is a stub section, if you can contribute please reach out.)

Hand sculpting can be done with numerous materials, from wood to plaster to clay. Anything used should be sulfur free. Popular sulfur-free clays include Sculptex and Monster Clay.  There are many different types of materials out there, so be sure to always do a spot check on sculpting materials before using them and before making a mold from them to avoid cure inhibition.


  • Wide variety of materials and varying costs
  • Budget friendly for beginners
  • No printer, program, or mechanical repair knowledge required


  • Symmetry, textures, and details can be tough to get uniform
  • Have to spend more time smoothing out nail marks, fingerprints, etc
  • Fragile masters. Very time consuming to resculpt if your original master breaks, can't just reprint
  • Have to manually create additional sizes of toys

Starting Tips

If you are just beginning - take small steps! Hand sculpted masters can be fragile, and there is a lot that can go wrong when you are just starting out in the realm of silicone. It's recommended that you begin with small and simple shapes until you get the hang of it, so you don't risk losing hours of hard work if you don't get a successful first mold.

Aluminum foil and armature wire can be used to help reduce the mass needed for a number of sculpting clay materials, keep its overall form without the material weighing itself down, and can help for an even bake or cure to reduce cracking. Refer to your material's packaging for instructions about ideal thickness, baking time and temp, etc.

Sculpting clays like Sculptex are often much firmer than what a novice sculptor is expecting. This firmness can be reduced by working the material with kneading and applying mild heat. Once worked, larger details and shapes can be more easily applied. Allowing the clay to sit overnight will result in it firming back up so it becomes easier to apply detail work.

Smoothing the Surface

The silicone molding process will pick up near-microscopic details of masters. Tiny scratch marks or even a thumbprint can, and have, noticeably transferred through all the way to a finished toy. Fingerprints and fine marks can be erased by using a solvent (either isopropyl alcohol or isopropyl myristate) applied to a cloth or q-tip and gently swabbing the surface. The solvent will slightly dissolve the clay and evaporate, providing a smoothing effect. Using a higher concentration will provide a stronger effect. Isopropyl alcohol is recommended for use with Sculpey (not to be confused with Sculptex) before baking, and isopropyl myristate is recommended for modeling clays; but please note that the contributor of this information has not personally tested the latter.

If you work Sculpey, you can use Liquid Sculpey to help fill in crevices. After the sculpt has been baked, you can also carefully sand or apply some surface finishing methods described below, but be sure to wear protective gear when sanding or spraying the master. When trying a new surface finish, always practice on a tester before committing to the method on your handsculpted masterpiece.

3D Printing

3D printing is the most common method of producing the master. The two main methods of 3D printing a master are FDM and SLA.

FDM Printing

This is the type of printing where a spool of plastic is fed into a hot end and squirted out onto a build plate. TwoTrees has an explanation HERE


  • Printers and material are cheap
  • Can be used for masters and mold shells
  • Fumes created by printing process are not nearly as bad for you
  • Post-processing does not require alcohol or exposure to nasty chemicals
  • FDM materials do not cause cure inhibition and are not going to contaminate your workspace


  • Lots of moving parts. Potentially lots of troubleshooting.
  • Longer active post-processing time due to sanding down layer lines and printer texture.
  • SLOW 3-7 day long prints

FDM printing is a great place to start from. The printers are inexpensive and the build quality has improved significantly in the last few years. They also don't expose you or the workshop to dangerous and cure-inhibiting chemicals like SLA printing does. When starting with FDM printing, you may want to start with PLA as it is one of the easiest materials to print with. It doesn't curl or generally have bed adhesion issues. The biggest downside of PLA is that it is a very hard material and sanding the printer texture out will take much longer than finishing a resin print off an SLA. It will also take much longer than finishing an ABS print. ABS is harder to print because it shrinks as it cools, but it is easier to sand and can be smoothed to a glass-like surface using acetone vapor. Searching for how to smooth ABS with acetone will return many results, but there are three things commonly left out of these tutorials you should be aware of:

  1. Acetone can form explosive vapors
  2. Smoothed prints must be allowed to completely off-gas the acetone before mold build (3-5 days)
  3. Acetone-smoothed prints will shrink and probably crack over a few months, so cast a solid resin master (smoothcast is a great choice) out of the first mold ASAP

There are some DOs and DONTs available HERE from ShopDad

SLA Printing

This is the type of printing where the part is made in a vat of liquid resin. Formlabs has an explanation HERE


  • FAST <1 day prints
  • Very high resolution for minimal printer texture = shorter active finishing time
  • Prints can be made very strong and long lasting
  • Less moving parts to troubleshoot


  • Nasty chemicals and fumes. Water washable resins are NOT safe because they can be washed with water. They can even be more dangerous
  • Waste must be properly managed and can not be thrown in trash.
  • Vat leaks tend to brick machines
  • Resins are strongly cure inhibiting and can be sneaky about getting on hands and then onto masters
  • Smaller print volume for the price

SLA printing is amazing technology that can produce a highly detailed master overnight. It also uses very nasty chemicals that are dermal skin sensitizers. This means that your reaction to exposure gets worse over time. Initially, you may not mind the funny smell or may not develop a rash from getting a little resin on your fingers; but with repeated occupational exposure you can be sensitized to the point where even mild exposure causes a painful and long-lasting rash or persistent lung problems. Water washable resins are NOT safer. Changing the diluent in the monomers to make them dissolve in water can mean an even worse sensitizer than with regular resins. Water and alcohol used to clean parts CANNOT GO DOWN THE DRAIN. You need to process it as much as possible and take it to your nearest waste management company for proper disposal. This can be done by evaporating off the water/alcohol and putting the leftovers into a sealed and labeled bucket. Care must be taken when handling unfinished resin prints that resin is not transferred from the print to anything that will touch silicone, as it is a strong cure inhibitor. If you find oval or crescent moon shaped areas of cure inhibition on a new mold, it is possible this is from touching an unfinished master and then touching a finished master the mold was made from. With good hygiene and patience, SLA printing is fairly easy to pull off and the results look great. Consider starting with a small machine for teenies since you will likely brick your first resin printer during the learning curve. There is a walkthrough that has an example of finishing a resin print in the instructions for the packer project. There is also a write-up for setting up a new Mono-X which is an inexpensive and popular machine. There are also some DOs and DONTs available HERE from ShopDad

With any type of 3D printing it is important to be patient. Your master will make a dozen molds and those molds will make a thousand toys, and all those toys will use tens of thousands of dollars in silicone. It is better to spend weeks at this first step than to rush it for the dopamine payoff of your first sale. Also consider that there is a difference between active time and inactive time. Active time is time that you must spend actively doing work. Inactive time is the time that work is being done but not by you. When starting a shop there is no limit to inactive time available. It is perfectly fine for a printer to take 5 days or curing silicone to take four hours, since you are free to work on other things while that happens. There is a huge limit on active time, however. Using a fast profile on a 3D printer that produces a lower quality part (requiring more touch up work and sanding) or strains the printer and increases the amount of maintenance needed is never worth  getting your print in hand a little sooner. Additionally, most 3D printed masters will be painted to create a nice surface finish and seal them. The cure time on the paint should never be rushed. Paint that is still off-gassing solvents will cure inhibit the silicone mold. Masters that have layers and layers of primer followed by an enamel paint do not need 24-48 hours to full cure, they need 1-2 weeks. Always spot check for cure inhibition on masters, because once you build the first mold the silicone will leave behind a nearly impossible-to-remove layer of silicone oil that will prevent you from repainting the master.

Surface Finishes on Masters 💚

The two main determinants of the final surface of the toy are mold release and the surface finish of the master. Mold releases such as Mann 200 set an upper bound on how glossy a toy can be. The aerosol spray leaves behind a satin gloss finish on the silicone of the mold which transfers to a satin gloss on the toy.

This is an unfortunate, necessary evil in most cases as the silicone used for the toy will attempt to bond to the silicone used for the mold unless a releasing agent is used. It is possible to make molds from other materials that do not require a release agent, such as many epoxy materials or Smooth Cast. The general rigidity of these materials limits what shape of toy can be removed from the mold. There is also a flexible urethane mold material by Smooth-On called Compat 45 which tried to fix these issues. It is not generally recommended within the indie toy community as it imparts a urethane / plastic like smell to the toys that some customers can detect. That smell indicating a chemical has been transferred to the toy along with an SDS that warns Compat contains carcinogens makes its use a red flag for many people.

Luckily, silicone molds can still reproduce a wide range of finishes and textures that get pretty close to a gloss even with mold release, and most enamel paints will be non-inhibiting when fully cured. There are also many different preferences in textures amongst customers, so whatever you go with will have a market. For testing different finishes there are files for making mini molds with a six sided fast printing insert HERE Using test swatches before going into full production is highly recommended. It will not only give you the best idea of what is possible, but also will help to get a feel for what causes cure inhibition and other issues before investing hundreds of dollars into molds.


The highest gloss attainable with silicone molds and Mann 200 release spray


One of the least glossy casts created using a master sprayed with Rust-Oleum Textured enamel paint

The trade-off in surface finish is that the glossier a master is, the more the colors will pop and mica will sparkle; but the more matte the surface is the better it will hold lube and the more comfortable it will be to use. This is a generalization, as some colors still pop quite well on a matte surface and some people find high gloss toys to be perfectly comfortable to use.

Here are a few examples of surface finish types with pros/cons.

Abrasive Media Blast (Sand blasted, but don’t actually use sand): The most matte finish with a velvet feeling.

Incredibly DurableExpensive equipment (12CFM or above compressor)
Soft velvet finish similar to the highest end vibratorsSilicosis if you use cheap media and don’t wear a respirator
Super easy to applyLoud and Dirty
Easy to remove scuffs / scrapes with a re-blast 
Cleans the master as it finishes it, can be done in dirty environments 

Glossy Hard Coat (Spray or liquids. EX: XTC3D): The glossiest finish on a master, producing a sating gloss finish on the toy.

Incredibly DurableCan use extremely dangerous chemicals
Easy to remove scuffs / scrapes with a bufferRequires a super clean environment for application
Can be polished to mirror gloss shineLiquid versions erase some detail
 Release spray limits gloss level to Glossy Satin

Vacuformed Mold: Not a master finish type, but one of the ways to get a glass smooth finish on a toy.

Can achieve very glossy finishesVacuforming equipment required
Molds don’t require release agentKnowledge of DFM needed (most designers will not know how to make toys that work with this method)
Mold production is incredibly high (molds take minutes to make)No need to repair, make another mold for ~$5
Molds are effectively permanent 

3D printed (ABS FMD) with light vapor smoothing: Not a master finish type, but one of the ways to get a glass smooth finish on a toy.

Can achieve very glossy finishesOnly suitable for some toy geometries
Molds don’t require release agentVapor smoothed ABS cracks over time
 3D Print lines visible

Rust-Oleum Black Enamel (The cheapest and most basic cans, NOT the advanced formulae): Fairly glossy finish with less chemicals and flops on the master.

Second glossiest finishFinish is relatively soft and dents / scuffs easily
Reasonably easy to applyCannot be repaired
No nasty chemicals or surprise dangersRelease spray limits gloss level to Glossy Satin

Rust-Oleum Hammered Spray Paint: An interesting hammered / gloss finish that is underutilized.

Unique hammered textureLong cure time – 2 Weeks
Reasonably glossy finishCannot be repaired
No nasty chemicals or surprise dangersRelease spray limits gloss level to Glossy Satin

Krylon Chalky Finish Chalk Spray Paint: Velvet matte finish.

Nice Satin finish (after mold release application)More difficult to use and sand than primer, same finish
High DetailCannot be repaired
Slightly more durable than primer, same finish 
No nasty chemicals or surprise dangers 

Rust-Oleum Textured Spray Paint: Rough gravelly finish, stimulating in soft silicones but abrasive in firms.

Unique high texture finishLong cure time – 2 Weeks
Easy To ApplyCannot be repaired
No nasty chemicals or surprise dangersErases some detail

Rust-Oleum Red Filler Primer: Beautiful velvet finish with extreme ease of application.

Nice Satin finish (after mold release application)Slightly less durable than Chalky Finish paints
High DetailCannot be repaired
Very forgiving to use 
Exceptional coverage ability 
No nasty chemicals or surprise dangers 

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