Several years ago, we wrote a short article describing how to make embossed pictures and lithophanes. We feel like it’s time to refresh, expand, and update older articles, as there are plenty of newcomers in the community, and also many things have become easier and more user-friendly since then. This time, we’ll show you several useful tips on how to make pretty cool things with filament color combinations. We’ll tell you how to mix filament colors into various shades or make a nice smooth color gradient in your lithophane projects. With just a little bit of trial and error, you can 3D print great-looking pictures, with no need for postprocessing. And we also want to talk about the HueForge app, which is a great companion for printing colored pictures as it helps a lot in choosing the best filament colors for any project.

Emboss like a boss

First, let’s start with one of the simplest applications for color change and playing with color combinations – embossing. This useful feature can be used for various logos, patches and other models that need to be printed multicolored (with no need for using the MMU3 upgrade). Previously, the embossing process took several steps before you could transform a picture into a 3D-printable object. Now, you can skip most of them thanks to the PrusaSlicer .svg embossing tool. When you import the file, PrusaSlicer allows you to edit it as if it were a solid object. You can adjust thickness, orientation, scale, etc. It’s really easy – give it a try! You can simply follow this guide.

Svg import tool (left) and a preview of the sliced embossed picture with color change (right)

And if you don’t have a .svg file, don’t worry. There are free programs that let you transform .png or .jpeg images into more editable .svg format: Inkscape, and Adobe Express, just to name a few.

Lithophanes 101

Now, let’s focus on more complex shapes: lithophanes. In its most basic form, making lithophanes is quite easy. Simply use any lithophane tool available online, such as Image to Lithophane by 3D Printing Rocks, and print the model with translucent filament, such as Prusament PLA Vanilla White. With backlight, you’ll get black & white photography. But we can do much more with color change: lifelike pictures, colored graphics, and lithophanes, all with multiple colors and shades. How? By playing with filament transparency and color gradients.

Useful tips for printing B&W lithophanes:

• Print in thin layers (0.1 mm) and with at least 90% grid infill
• You can color the printed model to make it more realistic.
• You can add more contrast by setting a color change and adding one or two layers of darker color on top of the model.

Filament colors and transparency

You probably remember color mixing basics from elementary school: when you mix red and blue, you’ll get purple, etc. Or, you may have noticed our color calculator on the Prusament Resin Color Kit product page – here you can learn even more color combinations. But, how does this color mixing apply to filaments?

Well, every filament has a certain level of translucency. When printed in thin layers, it can act as a color filter, similar to those used for photography. By checking this table, you’ll learn that material transparency is something that can be quantified and this is also why HueForge asked us to measure these parameters for their app – to populate the library. While these values may be usable specifically for HueForge, they may also give you a hint on which filament is more transparent than another. The values in the table get a score from 0,1 to 100. 0,1 is the least transparent filament (every carbon-filled Prusament, for example) and 100 is the clearest filament (Clear PETG, for example).

This means that when you take dark filaments with the lowest values and print them over any other color, no matter the thickness, the bottom color will mostly disappear as these dark filaments make an almost impenetrable barrier for light. On the other hand, when you print a clear filament in a thin layer over any color, the color will hardly show any change as the light easily passes through the clear layer. Obviously, these effects are more or less visible with various layer heights.

By the way, having everything measured by the HueForge standards is quite a big deal, because now you can preview our filament combinations and resulting colors without guessing! So stay tuned to learn more.

A nice example of filament transparency: Notice how the Prusament PLA Oh My Gold is transparent. When printed in one layer, it gets a hue closer to the color below (PLA Lime Green). Here, its color turns slightly greenish and gets more gold with more layers. The same thing is slightly noticeable on the Prusament PLA Pristine White in this photo.

With this knowledge, you can use various colors as filters with different properties. Again, if you take a red base layer and spread a thin layer of blue over it (or vice versa), you’ll get purple. The shade of the purple color can be slightly more red, or slightly more blue, depending on the top color’s translucency level and thickness. And this principle can be applied to almost any color of filament there is. And luckily, our Prusament portfolio has grown a lot during the last few years so you can go wild on the color combinations!

A nice example of a very simple color combination can be seen on the rubber patches I printed earlier for Stalker-themed LARP games. There, I was limited by flexible filament colors available in our e-shop, so I had to mix them and play with translucency. For example, the orange color on these patches is a mixture of two thin layers, where one is red and the other is yellow (I didn’t have any orange flex). Also, the blue shade gradient was achieved by mixing blue layers with black, or white.

Another great example of a color gradient made with translucency: First, look at the background. This warm yellow color is something that the Prusament PLA portfolio doesn’t offer at the moment. But printing one layer of Pineapple yellow over Prusa Orange will result in such a tone. Second, notice the man’s glasses. The color transition from dark orange to pale yellow is amazing, isn’t it? And it’s very easy – it’s just a dark background, 5 layers of Prusa Orange, 5 layers of Pineapple Yellow, and on top of them sit 3 layers of Vanilla White PLA. A similar gradient can be done with almost every color with suitable transparency.

Picking the right color

But how do people choose the right colors for the lithophanes? Well, we won’t lie to you. It is a little bit of an alchemy. It’s quite easy for black & white gradient but getting more colors requires some testing and experience. It can be guessed by just using a PrusaSlicer color preview but it will not give you any hint on the filament transparency and the resulting color combination. Luckily, there’s a HueForge app that is quite helpful for both beginners and experts in this field. This is an app that contains a huge database of filaments and their transparency values. Thanks to this feature, you can see a preview of the model before printing it. Plus, you have the option to adjust multiple things, like light source, lithophane shape and size, and much more. They have several video guides online that will help you to become a pro as fast as possible.

Note that our Prusament portfolio is in the HueForge too! And as we said, we even added the measured transparency values to our online help website, just for you to compare the material properties. And why is it good to have the filaments measured and added to the HueForge program? Well, now you simply can take any photo, choose the Prusament colors you have and with HueForge‘s help, you’ll be able to 3D print strikingly beautiful colored images in no time. The program will guide you to make the best color combination to make the final result as close to the original colors.

Example of HueForge process: Source image (top), HueForge color preview (middle), 3D printed colored lithophane (bottom). Note that we used a red layer instead of rPLA algae pigment, which resulted overall in more red tone than in the preview. Used colors (bottom to top): Prusament PLA Galaxy Black, Lipstick Red, Prusa Orange, Oh My Gold, Pristine White.

A few extra tips

Finally, we have a few extra tips for you. These might be helpful for both simple experimenting in PrusaSlicer and advanced coloring in the HueForge. We learned these things the hard way so hopefully, you won’t have to make the same mistakes. 🙂

• Print it with Standard PLA materials. You’ll shortly find out that most lithophanes are rather complex models that are hard to print with filaments other than PLA. And combining colors in thin layers is also something you don’t exactly want to do with other materials such as PETG. Wood-filled or otherwise altered filaments are not a good choice either, even if the bonding polymer is PLA.
• Keep the filaments dry. Or you will face A LOT of stringing.
• Print in thin layers. The smoothest gradients can be achieved by using the filament’s translucency, which is most noticeable in thin layers. But there’s an increased risk of failure.
• Expect the unexpected colors. To be honest, most of our projects turned out to be different than what we would expect. Not in a bad way, but different. It is challenging to get the right color combinations and the previews in programs may differ from what you’ll see in the real world. Even in HueForge, there are some small differences from real 3D prints.
• Avoid 3D printing pictures that are way too complex. The easiest lithophane is one made from black & white pictures with simple shapes. Printing a highly complex photo with bright and dark spots in all colors imaginable and parts both sharp and blurred, is hard, if not impossible.
• Save time for tweaking. Did we forget to mention how many times we failed? It takes some time and a lot of trial and error to learn everything.

Here’s an example of a few errors in one picture:

1. One layer was printed with rPLA Corn Pigment. This filament is not great for printing in thin layers with many retractions. A standard PLA would be better.
2. All of the used filaments were old and full of moisture. It caused a lot of stringing.
3. We expected the rPLA to be less transparent and the PLA Prusa Orange to be more transparent. The entire image was supposed to be more yellow/beige and less orange. Here is one of the few previews, where HueForge visualization slightly deviated from the real colors (see the HueForge preview below).

It is possible to adjust the filament transparency values in the HueForge according to the real result. Below is the preview with color transparency values altered to appear closer to what we printed. Notice the highlighted (changed) transparency values for Prusa Orange and Corn Pigment PLA. Note that in most of the cases, this is not necessary and it is possible that we actually missed some user error we made on the way. HueForge transparency values are measured well and usually work just fine and no tuning is necessary.

Finally, we used these adjusted transparency values to set the color change differently and reprinted the model. All it needed was to set the color change to orange just one layer lower. The result is still not great, but the orange hue was dealt with and the color combination is much closer to the original photo, see below.

The old model has 2 layers of Prusa Orange (left), compared to the new model with just 1 layer of Prusa Orange (right). The newer model’s colors are closer to the original picture.

Now, how do you like filament color mixing? Was this article helpful? We hope to see the beautiful creations you make with color change.

Happy printing!