Dual-Colour PLA Under the Microscope

Seeing the difference between high resolution (0.07 mm) and lower resolution (0.25 mm) layer height on a 3D print using dual-colour filament

Dec. 31, 2022

By: Erin

Introduction

The dual colour 'quantum' PLA by Matterhackers produces visually interesting results similar to iridescence. With this material, the alignment of the model on the print bed results in where on the model the colour transitions are when rotating the print about the z-axis. This was true for both models and various test prints. Curiously enough, the lower resolution print had noticeable colour ‘striations’ along the z-axis at some portions of the print. What exactly is going on here? Let’s take a look under the digital microscope.

Setup

• A simple $30 USB microscope was used. Magnification of the microscope is estimated to be at 40x (this is unverified however).
• The model used was Gengar by MetalheadPrinting on Thingiverse.
• Blue tack was used to help keep the print in place while observing with the microscope.
• Filament used is the Matterhackers Quantum PLA 1.75 mm diameter, ‘blue raspberry’ colour.
• Printer is the Prusa Mini+ with the satin build plate and assembled from a kit.
• 0.4 mm nozzle was used

Calibration

Calibrating the model angle was completed first using a calibration coin.

Method

One print was sliced at 0.07 mm layer height (3h 27m), and the other at 0.25 mm layer height (1h 7m). The model orientation and location was the same for both of the models. The filament was not changed or moved between either print. The prints were labeled on the bottom foot which corresponds to an internal print tracker spreadsheet. The USB microscope images were viewed on my computer.

Results

Discussion

The lower layer resolution means the filament isn’t being ‘squished down’ as much. This gave more space for both strands of colour to be visible. The combination of this over multiple layers gives the visible ‘striation’ effect.

After extrusion, each colour takes up 0.2 mm based on the 0.4 mm nozzle. With the layer height being 0.25 mm for the lower resolution, this means there is less tolerance for any twisting in the strand of extruded material. With the higher resolution layer height at 0.07 mm, the tolerance for twisting is increased because the filament is being ‘squished down’ more.

From this reasoning, a smaller nozzle would likely perform better at larger layer heights. However, the smaller layer height plays an important role in the visual effect of the piece, as discussed below.

Overall, the higher resolution print is fascinating to look at in real life due to it not being recognizable to many other things seen before. The layer lines are hardly visible to the eye, giving it a uniform appearance. It looks interesting based on how it reflects light and the colour change - both qualities involve picking up the object and rotating it. This reminds me of the Hackaday Prize project “Affordable Reflectance Transformation Imaging Dome” by Leszek Pawlowicz (more info).

There’s more to experiment with on this visual effect. Concave surfaces, convex surfaces, faceted faces, smooth faces, patterns in x-y, patterns in z, light source and direction. Going further, how could the visual effects be measured and quantified? Probably about reflectance, perhaps inspiration from radar reflectors can be taken, as well as the imaging dome above.

Imagine in the future where instead of colours that are mixed, it could be material properties. Perhaps dual-strand PLA with TPU to create resilient pieces that don’t shatter as easily. Obstacles to overcome in this approach would be the printing profile (temperature, flow rate, speed), as it would have to take into account both materials. Multi-material printing with an independent extruder (IDEX) approach would overcome that obstacle. The BCN3D Sigma D25 and Prusa XL come to mind.