Here at Pinshape, we have an appreciation for shiny things, so we’re doing a tutorial on polishing and finishing techniques for metal filled filaments. These techniques open a world of possibilities for surface finishes on 3D printed parts.
Before you get started, you’ll need some tools for polishing and oxidizing your parts. Sandpaper and steel wool are for polishing, and brasso and salt and vinegar mixture are for oxidizing.
Tools to Get Started:
- Metal Filament: We’ll be using ColorFabb’s Bronzefill and Copperfill which are made up of about 40% metal powder and 60% PLA filament.
- Sand Paper: A few different grits of sandpaper should do the trick; we used 150, 300, and 450
- Steel Wool: A few different grades of steel wool are useful as well; we used a coarse, medium, and fine.
- Brasso Metal Polish or Salt and Vinegar Mixture: This will be for if you want to oxidize your parts after polishing.
- Acrylic Spray or Epoxy: This is for sealing your parts after they’ve oxidized.
Step 1: Sand & repeat to remove layer lines
The first thing we’ll be doing is polishing. Right off the printer, your parts will be a bit dull looking. We’ll want to start with the lowest grit sandpaper. We used 150 grit to sand away all of the layer lines. Be forewarned that sanding doesn’t produce terribly much shine but it’s critical for later steps. After 150 grit, move up to 300 or so and then up to 450. After sanding, you print won’t be terribly shiny but it’ll be nice and smooth.
Step 2: Use the steel wool to give it shine
Now comes the more rewarding part. Steel wool really helps to bring out the metal particles and give your print some shine. Much like we did with the sandpaper, we’ll start by using the coarse steel wool and move our way up to the finer type. You’ll start to notice a fair bit of shine with the coarse steel wool and once you reach the fine grit, your part should positively dazzle. Now if you’re just looking for some shine, feel free to stop here but one of the most interesting properties of metal filled filaments is the ability to oxidize them.
Step 3: Treat your model with an oxidizing agent
There are a few options for oxidizing agents which will produce different results. The two we tested were brasso and a salt and vinegar mixture. Brasso is an ammonia based compound that is an extremely strong oxidizing agent but also comes with some health risks. Salt and vinegar is a little more benign and to make your solution, mix salt and vinegar in a spray bottle until the solution is saturated and salt will no longer dissolve (super scientific, we know).
If you’re going the brasso route, just wipe the compound onto your print in the locations you’d like it to oxidize. You can control the oxidation by varying the amount of brasso you apply. You should notice notable oxidation within about half an hour.
The salt and vinegar solution is a bit more subtle. You’ll want to spray your part and should notice oxidation within a few hours. Salt and vinegar isn’t as strong an oxidizing agent as brasso so to develop more of a patina, continue to spray your part every couple of hours.
Step 4: Add Finishing Touches & Sealant
After your print is oxidized, you can further finish it by using steel wool to dull or remove some of the oxidation and create some truly awesome looking parts. Your prints will continue to oxidize at a slower rate simply with exposure to air so to seal them, we recommend an acrylic spray or epoxy.
That’s all there is to it! There are a number of different metal filaments including those filled with iron, brass, and stainless steel (Proto-Pasta has a line of iron and stainless steel filaments). Each of these will behave a bit differently when oxidized. Iron for instance develops a rust and brass will often form a darker patina than those seen on bronze and copper.