Saturday, February 8, 2020

Mold lines are the bane of my existence

This afternoon I was putting some models together, cleaning mold lines, and doing some basing. Mold lines are a long-running antagonist for my hobby activity. I hate them when I am painting minis, so I will do my utmost to get rid of them. Even if I've started painting a model, I have been known to grab the razor knife or some files to fix a lingering line.

Back in the day, when most figures were single-piece models with filled undercuts, mold lines were easy. Find the seam, follow it around the figure with files and razor knife, done. Even most multi-part models are easy. Just find the seam on each piece and you're home free.

Lately I'm seeing a shift though. Mold lines are getting harder to remove. And it all goes back to the original design and manufacturing of the model.

More models are being produced based on digital designs that are then produced on a 3D printer, cast to make a mold or molds, and then cast to produce the figures and/or parts. The results are generally great models with a lot of intricate detail. Often the manufacturer will go the extra length and pre-assemble the figure for you. Most manufacturers are not going to take the time to smooth mold lines. They are interested more in producing however many figures and then moving on to the next project. This is especially true for manufacturers that are producing board game figures or mass runs of custom minis that are designed to be cheap to produce and inexpensive to buy.

I am not knocking these figures by any means. I have a couple of massive board games with minis that I plan to paint. And I have backed (probably a few too) many Kickstarter projects for minis. I am buying modern figures and will continue to do so.

I am noticing the difference between physical sculpting and 3D digital sculpting, and I will always prefer the former. This is simply because a physically-sculpted model has had to have a tool create all of the undercuts and depressions on the model. And if a sculpting tool had to get there, odds are I have a file, blade, or sharp tool that can get in there as well. I can get all of the lines.

Digital sculpting and casting are great for detail, but they often create mold lines that simply can't be removed. No physical tool has had to get into these depressions, nor could they. Instead, it's just a pointer for developing the model, and a liquid casting medium for making the mold. Models designed this way are not cast in metal; they're normally cast in resins or plastics. These flow into all of those crevices and create very smooth surfaces. Most are also forgiving when being demolded.

Metal models are very unforgiving. If there is a crevice that the metal flows into that isn't easily accessible, it will freeze the model in the mold. Sometimes the same will happen with resin or plastic, but it's much more correctable with softer material.

I have been getting around some of the mold lines by removing them as best I can with curved sculpting tools, but I have as likely as not gouged the surfaces and created worse blemishes than the mold lines. So then I have to go back and fill the area with sculpting putty and sculpt a new surface that fills the holes and blemishes. This creates a lot of work and occasionally results in models developing a propensity for flight.

Anyway, just something I was thinking about as I was working on some models today. Let me know if you have similar problems pop up with your figures and what you're doing to take care of them.


  1. Coming in a little late here, but those weird curved scrapers that dentists use to get plaque off the difficult places in your teeth work wonders for this. They can be a little hard to get ahold of though.

  2. Mould lines are the spawn of the Ruinous Powers.
    I agree with Unknown above about dental picks, and I'm fortunate in having a dentist for a good friend who hooked me up with a bag of old gear.
    BUT, *these* are one of the greatest things ever invented for resins and plastics!:

    I bought a couple of the Asssorted Packs from Albion Alloys and, yeah, point these things at mould lines and it's like watching Sororitas melt heretics.