Updated May 30, 2020
In this essay, I’m going to give you my top tips to executing generative art with a plotter. As a long-time generative artist, most of these findings are a result of my own personal trial and error with pen plotters. But before we dive into the tips, let’s talk about the tools first.
For my plotting, I like to work with the AxiDraw plotter from Evil Mad Scientist Labs. Although it hasn't been perfect, it's well made, easy to repair, and well documented. If you want to start plotting artwork, I'd suggest starting with one of these. With that said, a lot of my advice probably applies to other plotters, too. I'm also going to describe how to create designs for the plotter using Processing, but anything that can produce a PDF or SVG should work.
1: GENERATE ART WITH PROCESSING
Set your renderer to PDF. When running the plotter through Inkscape (more on this later), the PPI/DPI will be 72. If you want to plot an image at the maximum size of 11 x 8 inches, this means you'll set the size to 792 x 576.
Here's an example Processing sketch that will draw a single line:
import processing.pdf.*; void setup() { size(792, 576, PDF, "filename.pdf"); } void draw() { line(0, 0, width, height); exit(); }2: USE INKSCAPE TO DRIVE THE PLOTTER
If you're using Linux or Windows, you'll probably want to use Inkscape to actually drive the plotter. They recently announced native support for OSX in version 1.0 as well, and the creators say that it generally works, but they aren’t fully recommending it as of May 4th, 2020.
The first step is to setup the AxiDraw extension in Inkscape as documented on the AxiDraw site.
Then, open the PDF with Inkscape. Export it as an SVG. Somewhere in this process, a border gets added to the SVG, which I don't like. The document size also needs to be set in inches or centimeters (rather than pixels) to work properly with the AxiDraw. I wrote a small Python script that will remove the border and set the document size in inches. Feel free to use that.
Once that’s complete, open the edited SVG in Inkscape, and prepare to execute the plotter drawing.
EDIT: there's also an SVG mode in Processing that should avoid these extra steps. It's not working with my particular setup yet (through Quil, etc) but you could give it a try.
3: THE BEST MATERIALS TO DRAW WITH
As an artist, it’s your choice what materials you use. Below is a list of what I’ve tried so far, and what I’ve learned about each material.
Pens:
Pens are an excellent tool for plotter drawings. My preference is to use a Pigma Micron. These are extremely reliable, consistent, and durable. The plotter will be very tough on pen tips, because there are a lot of repetitive movements. Some pens will dry up mid-plot, but not the Microns. The AxiDraw doesn't apply any downward pressure beyond the weight of the pen itself, which might be a problem for some pen types. Also, Microns have archival ink, which is a bonus if you want your work to last.
Markers:
I like to use markers for plotter drawings almost as much as I like to use Microns. I've been using Prismacolor markers, which are expensive, but super consistent and smooth. You can get some beautiful effects with the slight bleed from the marker. Just like with pens, plotting is very tough on the marker tips, and your marker tips will be significantly damaged after a few plots. Stock up with a few of them to keep clean lines.
Pencils:
Pencils are a little trickier to use. With a soft lead, they become dull quickly. With a hard lead, the drawing tends to be very faint. Here’s what I’ve found works best:
Use a medium softness pencil (e.g. 2B). Get it very sharp, and use an extra rubber band on the plotter head to add a little bit of extra downward pressure. Then, babysit the plot, and as the lead starts to become dull, pause the plotter using the button on the side. Sharpen the pencil and place it back in the plotter, being careful to put it back in at the same height from the paper. Then resume the plotting through the Inkscape interface.
I've also done some drawings where I use a pencil for a faint layer and a pen for a dark layer, and that looked cool.
Brushes and Paint:
Using brushes and paint with a plotter requires much more experimentation. This is an active area of investigation for me, and it’s easily the most difficult medium to pull off. You need a game plan for how to reload the paint on the brush. I've been using a paint tray at the right-most edge of the drawing, and I systematically inject "lines" above the paint tray to have the plotter automatically reload the paint brush:
This requires a lot of manual attention and care, but the final product is neat:
I recommend using high quality acrylic paints, and keeping the paint in the tray thin and wet through frequent manual adjustment. For a paper, consider using a thick mixed-media paper or even a textured paper specifically designed for painting.
4: THE BEST PAPER TO DRAW ON
Your choice of paper for plotter art is very important. Plotting is not only tough on the drawing utensil, but also on the paper. When working with pens or markers, I use Bristol paper, which is thick and very smooth. When I tried paper with more texture, the pen tip eventually roughed up the paper surface and the pen nib was gummed up.
Additionally, you want a very smooth surface underneath the paper. I've been using a piece of whiteboard from Home Depot. I tape the paper down to this to ensure it doesn't move.
5. CONSISTENTLY ALIGN THE PLOTTER WITH THE PAPER
This is frustratingly difficult! If you have a pre-defined area you want a plot to fit in, it's hard to perfectly align the plotter so that the drawing ends up where you want it to. Here’s what I recommend.
First, if possible, wait to trim your paper until after you done the plotter drawing. Start out with a larger piece of paper that has extra margin on every side, and just do the plotter drawing in the middle of it. Then, it’s easy to trim it to the perfect size.
However, if that’s not an option, and you need to align as closely as possible with an existing drawing, border, etc, you’ll need to do an alignment check while setting up the plotter.
First, make two marks on your paper using a ruler of some sort. The first should mark the top-left (0, 0) corner of the drawing. The second should mark the bottom right corner.
Second, set up your plotter so that the initial position puts the pen perfectly on top of your first mark for the top-left corner.
Finally, open Inkscape, go to the AxiDraw Control extension, and switch to the “Manual” tab.
Using manual movements to align the plotter
Use the “Walk Carriage (X)” and “Walk Carriage (Y)” commands to move the plotter exactly the width and height of your drawing. Ideally your pen will be directly above the second mark once your plotter has been aligned. You’ll need to manually shift the plotter to align it. For best results, repeat this with the top left corner and then the bottom right corner again, making smaller adjustments each time.
This won’t give you sub-millimeter accuracy, but it should be a very close way to align the plotter with the paper.
6. DESIGN CONSIDERATIONS
When thinking about creating generative art with a plotter, the main aesthetic consideration you'll have to get used to is that you can't cover anything up -- everything is just lines. If you have a program that draws shapes, and you want those shapes to be "opaque" (covering things below them), you have to write code to do that all manually. That means checking everything for intersections. You might get some use out of a polygon clipping library like GPCJ (it's a pain in the ass to use, but it works).
Depending on your plotter, it may also be VERY IMPORTANT to not have it try to draw anything outside of the mechanical limits of the plotter. Newer AxiDraws handle this well, but the older ones made a horrible noise and lost track of where they were when this happened. I’m guessing many plotters may suffer from this.
Other than that, plotters are super high precision, and I suggest you take advantage of this. Exactly how to do this is a real art problem, so I'm leaving that to you to solve on your own. If you need inspiration, follow me on Twitter or Instagram for my latest works and experiments.
7. SPEED UP THE PLOTTING TIME
Plotting can be a length process. To make the drawing go faster, you want to minimize the movement with the pen raised between strokes. In my programs, I do this by first collecting every line I want to draw. Then, I do a kind of "sort" of the lines. I start with some line, then pick the next line by looking for a start point that is closest to the end point of the previous line. Repeat until there are no more lines.
Anders Hoff wrote a tool that will take an SVG and do this automatically, called svgsort. You may just want to use that.
EDIT: new AxiDraw software will apparently include a tool to do this as well
8. MAKE BIGGER WORKS
If you have an AxiDraw, you can only draw 11x8 inches at a time, or if you got one of the new larger plotters like me, maybe A3 (roughly 11 x 17 inches). If you want to make a bigger drawing than that, you either need a bigger plotter (either expensive or custom made, generally) or you need to split the drawing up into sections. I've used a few different approaches with this.
First, I tried out drawing the tiles right beside each other on the same piece of paper, thinking that I could position the plotter "perfectly" and everything would be seamless. This turned out to be impossible. With a pen or marker, if any lines crossed the tile boundaries, there was no way I could get those lines to be seamless, no matter how perfectly I thought I positioned the plotter.
So, for some works, I embraced the seams. For my largest plotted work, Understand, I went with a styled tiling pattern that didn't detract from the work. I drew the outline of each tile as part of the plotting process, then cut out the tiles by hand with a razor. Finally, I reassembled them with adhesive on a foam board.
(In general, embracing the “flaws” and limitations of your medium is a solid artistic strategy. It may sound cliche, but often you can turn weaknesses into strengths this way.)
For other works, I’ve generally tried to create designs that avoid having lines cross over sections. To make this look natural, your sections need to have a significant amount of overlap so that all curves can fall fully into one section or another. Unfortunately, this also puts an upper bound on the longest seamless curve you can draw, but that’s just the nature of the game.
9. EXPERIMENT
The last piece of advice that I have is that you need to experiment. Plotters have a steep learning curve at first, but the satisfaction of producing a real, physical piece of artwork makes it all worth it. There are so many interesting things you can create with a plotter, and most of them haven't been discovered yet. If you experiment and try new techniques, you'll quickly find fertile new ground.
That's all for now. If you enjoyed this, and want to be notified when I publish new articles and new artwork, feel free to sign up for the newsletter below.
Cheers!
