Short answer: Cleaning a miniature means removing three kinds of grime before you paint: mold lines from the casting seam, release agent oil left over from manufacturing, and finger oils from handling. First scrape the mold lines off with a blade or a dedicated tool, then wash the model in warm soapy water and let it dry completely. Always do this before priming.
It is an invisible step, but it is the one that decides everything. Skip it and even the most expensive paint will flake, primer won't grip, and fine detail disappears. The old hobby saying captures it perfectly: "a good paint job starts with a good clean." Below I walk through all of it, from spotting a mold line to washing resin.
What is cleaning and what does it do?
Straight out of the mold, a model carries three kinds of grime, and cleaning simply means stripping all of them off. First is the mold line: a thin ridge left where the two halves of the casting mold met. Second is release agent, the mold-release oil, which is especially heavy on resin. Third is the finger oil and dust you transfer just by holding the model.
What they all have in common is this: none of them wants paint to stick. That is exactly where cleaning comes in, letting paint and primer truly grip the surface. Removing mold lines also kills the ugly raised line that shows up under light colours and after drybrushing (a near-dry brush dragged over raised detail). So even though this is a beginner step, no professional ever skips it.
What is a mold line and why does it matter?
Let's start with where it comes from. Plastic, resin and metal minis are cast in two-part molds, and where the two halves meet, a thin ridge runs parallel to the surface — that is the mold line. On metal and resin, when it shows up as a thin film, it is called "flash."
You can barely see this ridge with the naked eye, which is why many people ignore it. But once paint goes on, especially in lighter tones and after a drybrush pass, it pops as a sharp line and instantly bothers the eye. It is most visible on flat surfaces: armour plates, cloaks, gun barrels. So start your cleaning there first.
The community's rule of thumb is blunt: a good paint job starts with a good clean. Removing a mold line before you paint is far easier than trying to rescue it from under dried layers later.
How do you remove a mold line?
The key thing to remember is this: the goal is to scrape, not to cut. You are bringing the ridge level with the surface without gouging the material. Pick the method that fits your model and the surface:
- Back-scraping with a hobby knife: Hold a sharp craft blade (X-Acto / Olfa) at a slight angle to the surface, not square to it, and drag it gently along the line. You're shaving, not slicing; this is also called draw filing.
- Mold line remover tool: A purpose-made scraper bevelled on one side. It's safer than a blade for beginners because it's far less likely to dig a gouge.
- Needle files: Small fine-toothed files. Great on metal minis and broad areas. On plastic, be careful — they bite fast.
- Fine sandpaper (600+ grit): For a final pass on broad flat surfaces. Use a very fine grit so it leaves no scratches.
Finish this before Priming & Undercoating, because a mold line you missed looks twice as obvious once primer is on it.
How do you wash and degrease a model?
Next comes degreasing, which means lifting release agent and finger oil off the surface. Resin models carry a lot of release agent from the mold, and that oil can completely stop primer from gripping. 3D resin prints also hold uncured resin and IPA (isopropyl alcohol) residue on the surface. Plastic and metal carry manufacturing and handling oils too. The fix is simple:
- Fill a container with warm water — never hot.
- Add a few drops of a grease-cutting dish soap (Fairy or Dawn).
- Gently scrub the model with an old, soft toothbrush; don't ignore recesses and crevices.
- Rinse with clean water and let it air-dry completely — usually a few hours. Never prime a damp surface.
For 3D prints, also make sure the model is fully cured; half-cured resin stays tacky and ruins paint. And once you've washed it, handle the model with gloves rather than bare hands, or you'll put the oil straight back onto the surface you just cleaned.
Do you clean before or after assembly?
This one trips people up, but the general rule is simple: clean first, then assemble as much as you can reach with a brush. The one exception is areas a brush can't reach — inner faces, undersides of wings, tight gaps. Leave those as separate pieces; this is called subassembly painting, and the full method is in Subassembly Painting.
Mold line cleanup, on the other hand, must happen before assembly. Once parts are joined you can't reach most of the seams anymore. To fill the join gaps you use liquid green stuff or modelling putty, and those get cleaned up and sanded once dry, before painting too.
How long does it take, and what do you need?
Here's the honest picture: cleaning a single figure takes 5 to 15 minutes, but a whole army adds up to serious time. On the materials side, you don't need an expensive kit; a few things from the kitchen cover half the job:
- A sharp craft knife (X-Acto or Olfa) or a mold line remover.
- A needle file set and 600+ grit fine sandpaper.
- A grease-cutting dish soap (Fairy, Dawn) and an old, soft toothbrush.
- A bowl of warm water and a clean cloth to dry models on.
- Thin work gloves — so you don't re-oil the model after washing.
- A dust mask for sanding resin; resin dust is harmful.
Most common mistakes
The sneaky thing about mistakes here is that they usually surface later, after the paint dries, and they're hard to fix. The most common ones:
- Painting before fully scraping the mold line; it shows up later and becomes nearly impossible to rescue.
- Priming resin without washing it first; the result is inevitably flaking.
- Using hot water; some plastics and resins warp.
- Handling the model bare-handed after washing and re-depositing oil.
- Pressing the blade square into the surface and gouging it by accident.
Pro tips
A few small habits both speed up cleaning and save the result:
- To find mold lines easily, hold the model up to a light source at various angles; the glare gives the line away.
- Once cleaning is done, touch the model with a dry brush, not your fingernail.
- Because resin dust is harmful, wet-sand and wear a mask whenever you need to sand.
- Painting a whole army? Work in batches: clean every model first, then wash the whole lot together. It also makes moving on to Zenithal Priming far smoother.
Frequently Asked Questions
Does a mold line really ruin paint?
Yes, it does. A line that looks trivial to the naked eye sharpens under light colours and after drybrushing, and on flat surfaces it instantly bothers the eye. Once it's buried under paint it's very hard to fix, because scraping now lifts the layers above it too. That's why removing it before painting is the only sensible path.
Do I have to wash every miniature?
For resin and 3D prints, absolutely; release agent can completely reject primer. Plastic and metal carry manufacturing and handling oil too, so washing is still the safest bet. Spend a few minutes with warm soapy water and you mostly eliminate the risk of flaking down the line.
Why warm water and not hot?
Hot water softens and warps some plastics and resins; thin parts can bend. Warm water, by contrast, is hot enough to cut the oil but gentle enough to spare the material. For the same reason, air-dry the model at room temperature after washing, not on something warm like a radiator.
How long should I wait after washing?
Until the model is fully air-dry, which is usually a few hours. Water hides in recesses and crevices, so don't rush it. Prime a damp surface and the primer comes out rough and won't grip. A little patience here means a clean foundation from the start.
I don't have a knife — can I still clean a mold line?
Yes, you can. A mold line remover tool is safer than a blade for beginners and far less likely to gouge. On broad flat surfaces, 600+ grit fine sandpaper also works. The point is to scrape, not cut: flatten the line without carving into the surface.
Is breathing resin dust dangerous?
Yes, resin dust is harmful and shouldn't be inhaled. If you need to sand, wet-sand so the dust can't go airborne. Wear a dust mask and work in a ventilated space too. These precautions are small, but they matter over the long run.
Key takeaway
In the end, cleaning is the invisible step that decides the outcome: scrape the mold line, wash the model in warm soapy water, dry it completely, and always do it before priming. Five to ten minutes of prep saves the lifespan and crispness of your entire paint job.
The right knife, files and degreasing supplies make this step far easier. To round out your cleaning kit, browse our paints, brushes & hobby supplies.