3D Printing post processes – Part 4: Adding colors and gloss

Even a full colored print deserves the artistic finishing touches. A printed piece can be spray-painted, hand painted for added effects and glossed for the optimized realism.

Avatar Bust
Avatar bust, 3D printed on Stratasys by Legacy Effects

In any case, the first step is to always ensure the model is free of dirt, oil, dust, moisture or defects; otherwise the paint would only have attached itself to the layer of foreign material. For added effects, lightly sand the model down before applying an undercoat to achieve some surface roughness, but without compromising on the details. Remember to clean the model of any dirt, oil or moisture before applying a layer of primer. The primer (undercoat) would ensure better adhesion of paint to the surface, as well as increase the durability of the paint.

In the case of 3D printed thermoplastic parts, however, we recommend primer before applying fillers, which will then be sanded down, to counter the layered look of FDM prints. Clean the wax and grease off the part and apply primer again. Repeat this process until you are satisfied with the quality of the part.

Layer sanding
Illustration of finishing effect on FDM surfaces


Another purpose of the primer is to reduce the numbers of paint coatings that would go over it because it would base the model into a neutral color. Reducing the number of paint coats will help reduce the loss of details as the layers of paint accumulates. Always strive to have several thin and consistent layers rather than singular thick ones. There are many methods to add color onto your creations, many processes to arrive at the picture-perfect piece.

Spray painting

Using a pressurized can of paint, this is the most time efficient method to apply color to any piece. Imagine having to coat a large area with thin and even coat of paint; Spray painting is the way to go. You can use taping methods to cover up areas which you do not want the next particular coat of paint. Another method is to perform airbrushing; it is likely to give more accurate spot painting, but it takes much longer to set up, as well as taking more experience to master.

Place the model on a cardboard or an open shell box before spraying to prevent tables getting messed up. Do your spray painting in well-ventilated area to prevent inhalation of toxic vapours. A good practice includes a pre-spray in the air to make sure there are no residual splatters and that the can is evenly distributing the paint. Allow the paint to set before applying the next layer.

Brush painting

The most elementary of painting jobs is to use the brush; it is a relatively easy skill to pick up, but one that is difficult to master. Thin down the acrylic paint with water such that it does not obscure the details of your prints.

Start by painting the basecoat with the dominant colors of your desired end product with steady but light sweeps. Do not fret the small details or you will end up with a thicker coat than required. You can always apply another consistent thin coat of base color. In cases of miniatures and art, use ink or extra-thinned black paint for realistic shading. Dry-brushing is also a great suggestion to highlight and accentuate details. Finally, using extra fine brush, touch up the small intricate details with diluted paint.

 

Liquid Dye and Powder
Liquid Dye and Powders used in Polyjet dying.

Dye dipping for Polyjet

Exploiting the fact that Polyjet parts can take in moisture if soaked for extended periods of time, one can consider liquid dye dipping for tinting of your end products. Dye dipping works best with transparent and translucent materials, such as VeroClear.

During the dying process, the model have to be free of support material, therefore, it would be advisable to soak the piece in a diluted (2%) caustic soda solution (NaOH) for about 30 minutes before rinsing with the waterjet to remove any remaining residue. After the model is set to dry completely, wipe it down again with isopropyl alcohol (>90%). Simply soak your prepared part in a mixture of common clothing dye and water water for 10 to 20 minutes before fishing it out to dry.

TIP: Higher powder to water ration results in deeper more intense dyed color. Apply clear lacquer after drying to enhance glossy feel.

Applying lacquer coat

Typically, the application of lacquer coating is done to improve on the clarity when transparent parts are involved. A truly clear part makes your printed model closer to reality and end product.

Sanding is recommended before the lacquering process as it would result in a more consistent feel, and also remove any support “puff-ups”. Using the recommended 800 to 1200 grit, rinse and clean the part of any dust, dirt or residue when you achieve an acceptable smoothness.  Leave it to dry completely before a consistent layer is applied. Do at least 2 to 3 swift coats of lacquers for better results. Too thin and the effects would not be visible; too thick and the lacquer would start forming liquid trails. When the lacquer coat is dry after approximately 20 to 25 minutes in well-ventilated conditions, flip it over to expose the underside and apply a similar layer of lacquer coating. Again, allow it to fully dry before polishing with dry cloth.

VeroClear Foot
Read more about our post process lacquering of the 3D printed medical foot!

For more information, please contact us.