Painting 3D Prints

Safety before color

Paints, primers, thinners and clear coats each come with an SDS. Read the one for the product in your hand. As an example, Rust-Oleum's SDS for a common aerosol enamel (Painter's Touch 2X Gloss Black, 249122) classifies it as an extremely flammable aerosol containing gas under pressure that may explode if heated, causing serious eye irritation, possibly an allergic skin reaction and drowsiness or dizziness, suspected of causing cancer, and causing organ damage through prolonged or repeated exposure. It says to use it only outdoors or in a well-ventilated area, wear gloves, protective clothing and eye protection, and use an organic-vapor respirator where airborne levels may exceed exposure limits.

• Ventilation and a respirator. Formlabs' painting guide says spray painting involves airborne particulates and solvents that pose health hazards, and to use a NIOSH-approved respirator in a well-ventilated workspace. The cartridge type comes from the paint's SDS; the Rust-Oleum sheet above names organic-vapor cartridges.
• Gloves. Formlabs suggests nitrile gloves, which also keep fingerprints off the model.
• Fire. Spray away from flames, heaters and sparks, and store cans as the label says.
• Brush-on paints are not hazard-free either. Their label or SDS sets the ventilation and glove advice.

Where to set up a painting area: Setting Up a Safe Workspace.

Prepare the surface

1. Remove supports and scars. See Removing Supports Cleanly and Sanding 3D Prints. Formlabs notes that on FDM prints with tall layers, sanding the whole model may be necessary to hide layer lines.
2. Assemble first where you can. Polymaker suggests priming parts fully assembled, sanded smooth and free of debris. Prusa's post-processing article suggests a test assembly with tape to plan which parts to paint separately. See Gluing and Joining Parts.
3. Clean off the dust. Formlabs washes parts with water and a soft brush (distilled water where water is hard, to avoid spots), dries them, then uses a tack cloth. Polymaker uses compressed air or a blower; do that outdoors or with dust protection, since it puts sanding dust in the air.
4. Prime. Polymaker calls primer essential for paint adhesion and starts with a flat gray primer or filler primer. Priming is covered in Filling and Priming.

Thin coats

The rule every source here agrees on: several thin coats, not one heavy one. Formlabs warns against pooling and against paints that clump into thick layers, and Polymaker warns that rushing drying causes clumping or uneven texture.

Step	Formlabs' spray method Starting point
Distance	About 6 inches, moving quickly while rotating the model
Color coats	2 to 3 thin layers to cover
Between coats	20 to 30 minutes once the coat is opaque
Clear coat	1 or 2 thin, even layers over a polished surface
Curing	Let paint harden at least a week before handling; wear gloves and handle gently if you must move it sooner

Those are Formlabs' numbers for the hobby spray paints it used. Your can's label overrides them, and Prusa's article gives a different spray distance (about 20 cm, 8 to 10 inches) for its filler and base coats. Formlabs also discourages hardware-store and fine-art paints for models because they clump and build thick layers.

Brush, airbrush or spray can

Method	Good at	Notes from makers
Spray can	Primer, base coats and clear coats on larger parts	Mask what should stay unpainted; Formlabs uses blue painter's tape pressed down firmly, and says not to leave general-purpose masking tape on for more than a few days
Airbrush	Even coverage and gradients on large surfaces	Polymaker says it is less precise than hand painting for fine detail
Brush	Small areas, fine lines, eyes, textures	Prusa's article thins brush paint with water and uses several layers to avoid brush marks

Detail techniques

Prusa's post-processing article describes three common model-painting techniques:

• Washing: heavily diluted paint applied with a soft brush and wiped off, leaving color in the recesses.
• Drybrushing: a flat brush with most paint wiped off on a napkin, flicked quickly across raised edges.
• Chipping: a sponge with a little paint, wiped on a napkin, dabbed lightly to imitate worn paint.

The same article paints the least accessible or largest areas first, and seals layers with a clear coat so later steps do not smudge them.

Match the paint to the material

• Flexible filaments (TPU and similar): Polymaker says to avoid acrylics because they crack when the part flexes, and to use paints made for flexible surfaces. See TPU.
• Resin prints: paint only after the part is fully washed and cured. See Finishing Resin Prints.
• Unknown combinations: test the primer and paint on a scrap print first.

Paint adds thickness too

Primer, color and clear coat each add a film. On a display piece that does not matter. On parts that slide, snap or screw together, mask the mating faces or test the fit after painting. See Fits and Tolerances.