As mentioned in a previous article (link), the soft plastic miniatures included in modern board games like HeroQuest, generally come with with a helping of multiple types of chemicals on their surface. The bare unprimed soft plastic figures arrive coated with mold-release agents, finger oils, and migrating plasticizers. The miniatures must be cleansed before being painted.
Manufacturing Process Contaminants
The plastic is cast in a steel mold, and in order for that mold to be rapidly emptied, refilled, and recast, it must remain virtually frictionless. That is where the mold-release agent comes into play. The mold release is applied through various methods to coat the inside of the mold. After casting, the miniatures are removed from the mold while still hot and left to cool slowly in bulk containers. They are not rinsed or cleaned prior to assembly or packaging. This process leaves mold-release residue on the plastic.
Manufacturing Materials Contaminants
Plasticizers, generally solvents, are combined with the resin used in the casting process to provide plasticity and flexibility and reduce brittleness. During the cooling process, they can migrate to the surface and mix with mold-release agents and finger oils (more on that shortly). This migration can also happen during storage
Generally, when these types of miniatures spend long periods of time in an airtight environment, the plasticizer can pool on the surface. This is very apparent on prepainted Mage Knight miniatures that remain sealed in their packaging for years. However, if these miniatures are left in an open environment with airflow, the solvents will evaporate, leaving a slightly greasy film.
Human Contaminants
Multi-part, preassembled miniatures must be built by hand. This process requires selecting parts from bins or clipping them from sprues and gluing them into place. If the individual performing this work is not wearing gloves, there will be finger-oil smudges and fingerprints on the miniature. Depending on personal habits, there may also be other residues. These oils are mostly invisible to the naked eye until the miniature is painted. They can prevent paint from adhering properly or may become visible as unintended surface texture.
The figures are assembled using quick-set adhesives, which vary by manufacturer. This adhesive can sometimes find its way onto the surface of the miniature.
Individuals who remove mold lines from these plastic miniatures often do so with bare hands. This process leaves fingerprints and skin oils on the surface. As with production contamination, these residues can affect the final paint job if not removed.
Results of the Unclean
All of these chemicals vary in type and can have different effects on skin, respiration, and paint adhesion. Without proper surface preparation, paint can bead, appear uneven, or peel away entirely, as happened in the case of the Mage Knight miniature. Quality control at many plastic miniature manufacturers does not appear to treat surface contamination as a concern, or it would be addressed during production. There are, however, a few notable exceptions—companies that produce pre-primed miniatures.
Pre-primed miniatures must be thoroughly cleaned prior to painting. Manufacturers of these miniatures understand this and perform the necessary preparation before priming.
How to Clean Soft Plastic Miniatures
Understanding the soft plastic material is key to cleaning these miniatures properly. Hot water and soap with a toothbrush can leave striations or abrasions in soft plastic. These appear as scrapes or unintended line details. Cold water can constrict the surface pores of the plastic and harden the mold release into a semi-lacquer-like state. So how should these temperamental, flexible plastic models be cleaned?
The first step is the the hot water bath as outlined in the article “Out, Damned Warp! Out, I say!”. That process allows the plastic to relax, returning it to its original molded shape while removing most surface and near-surface contaminants. The hot water bath may develop a slight rainbow film across the surface of the water. If this occurs, replace the water and repeat the bath.
After the hot water bath process the miniature is most likely safe to primer. However, sometimes the contaminates don’t like to release from the surface. Finger prints are notorious for this. The contaminant may have been trapped under an air bubble during the bath, hardened previously, or be resistant to the solvent effects of hot water. If this is the case, the next step should resolve the issue.
Isopropyl Alcohol Bath
Because fingerprints, many mold-release agents, and plasticizers dissolve in isopropyl alcohol, it can be used as a secondary bath. The process is simple and results in a clean, slightly more rigid surface ready for priming.
Due to its molecular size, isopropyl alcohol can penetrate small cracks and crevices in the miniature. Being a stronger solvent than hot water, it can dissolve more resistant buildups of oils and mold-release lubricants. It will also dissolve plasticizer at or near the surface, slightly reducing the flexibility of the plastic.
The entire process takes about 30 seconds per miniature. Durations longer than that allow the isopropyl alcohol to sink farther into the miniature and remove more of the plasticizer, which will increase the rigidity of the miniature as it dries.
The following warning is necessary because, well, there are some people.
Warning Isopropyl Alcohol
Do not drink. Isopropyl alcohol, sometimes called isopropanol, is a clear colorless, flammable liquid. It has a sharp unmistakable scent. The alcohol pouch wipes commonly used as an antiseptic in wound treatment generally have isopropyl alcohol as the active ingredient. It is broadly used as a disinfectant and cleaning agent. Toxic if ingested, inhaled, or absorbed through the skin. It requires ventilation and safe handling to avoid lung, eye and skin irritation. Use gloves and glasses for personal protection.
Tools and Setup
Only a few tools are required:
- Rubber, latex, or nitrile gloves
- Safety Glasses
- Bottle of Isopropyl Alcohol
- Container for the dipping.
- Chopsticks to handle miniatures
Practical Example: Bardsung Hob
The first image is of a slightly defused light reflection on the surface, most likely from the mold release, and the second image is of finger prints on the base . These survived the pass through the hot water bath.
Pour enough isopropyl alcohol into a container to fully submerge the miniature. Using chopsticks place the miniature in the bath for approximately 30 seconds. Remove it, again using chopsticks, and place it on a cardboard surface to dry. From this point forward, handle the miniature with gloved hands only to prevent further contamination.
Density and Duration
Thicker models or components may require slightly extended time in the isopropyl alcohol bath. Harder plastics, such as the Hob shown, may change shade slightly. Very resistant contaminants that cannot be removed by soaking may require targeted removal using a cotton swab saturated with isopropyl alcohol and gentle agitation. These cases are rare.
After the bath, place the miniature on corrugated cardstock. This material will help wick away excess alcohol. No rinse is required. Allow it to rest for 24 hours.
Safety Considerations
Working with isopropyl alcohol requires caution. Always take appropriate safety measures. Work in a well-ventilated area. Do not inhale vapors directly or ingest the alcohol. Wear latex or nitrile gloves to prevent transferring skin oils to the miniature. Keep a dry cloth nearby for spills. Allow miniatures to rest and off-gas for at least 24 hours.
After 24 hours, the miniatures should be ready for the next step. This delay accounts for variations in off-gassing time among different soft plastics.
This preparation leads directly into the next step: soft plastic miniature priming, which is covered in a separate article.
– Dru
Dru's Den of Ill Repute 