What type of marker is best for drawing on windows to prevent bird-window collisions?
Last spring, I started an experiment to find out the answer to this question, aiming to test 1) how easy markers are to apply, 2) how durable markers are if left on a window outside, and 3) how easy the markers are to remove from the glass.
The various marker types tested in the experiment. The coloured tape was used to associate the markers with the treated pains of glass. A list of these products is provided below.
This project was made possible by support from three sponsors: London Public Library generously sponsored the cost of purchasing 6 different marker types; Synergy Windows and Doors London provided me with panes of glass to use for testing the various treatments, and Feather Friendly contributed a roll of their DIY tape to use for comparison as a positive control (since the product is known to last on windows outside for at least a year).
The test setup was very simple: I left 5 panes of glass outside in my backyard, each treated with two different types of markers (one on each half). I drew vertical lines, spaced 5 cm apart, similar to the marker spacing required for effective collision prevention. The panes were all left leaning against a fence, tilted backward by about 20 degrees, exposed to part sun, with the treatment side facing out. The panes remained outside in the same spot for an entire calendar year, and were otherwise handled identically. I added coloured tape to the treated glass and to the markers themselves for identification purposes.
5 glass panes with various treatments applied where they remained for the past 1 year. Each treatment was applied to 1/2 a pane except for the furthest on the left. The pane on the right was used as a control (no treatment on half, Feather Friendly DIY tape on the other). This spot is partly shaded by a large maple tree, but the panes were still exposed to sunshine, rain, snow, etc.
Now, after a full calendar year, it’s time to find out which markers held up the best against the elements. Below I will evaluate each of the marker types that I used, and provide recommendations at the end. Before taking photos of the results, I relocated the panes of glass and put them in front of the black door to my shed to make it easier to see the remaining markings on the glass.
The video clips below show part of the durability test. I simply laid the glass flat, and ran my finger over it to see if the markers could be removed. A later (not recorded) part of the test involved spraying the glass with hot soapy water and wiping the markers off.
Video soundtrack by Circuit Wave.
Here's a summary of results (listed in the same order as they appear in the video above):
As expected, the Feather Friendly DIY tape held up beautifully and no markers were removed or degraded over the year outside. This control is excluded from the video and summary below.
1. Name: Flymax Acrylic White Paint Pen / Oil Paint Marker (marked in black tape)
Overall rating: 3/5 stars
Ease of application: Medium. A bit runny, ink did not dispense evenly despite consistent pressure. At a couple points, needed to shake pen to redistribute ink inside.
Durability: Medium. Marker faded in a few places.
Ease of removal: Wiped off easily with finger without leaving residue.
2. Name: Mr. Chalk Liquid Chalk Markers (marked in checkered tape)
Overall rating: 2/5 stars
Ease of application: Easy - went on smooth, no smudging.
Durability: Poor - mostly faded
Ease of removal: The little remaining on the glass wiped off with a finger
3. Name: Dixon China Marker, White (marked in green tape)
Overall rating: 5/5 stars
Ease of application: Easy. Applied pressure and had to go over a couple spots multiple times to ensure wax was applied uniformly. Not quite as bright as the ink options.
Ease of removal: Did not come off when rubbed with finger, but came off when scrubbed with hot water and soap.
Notes: The markers and packaging use minimal plastic.
4. Name: White Acrylic Paint Pen for Art (marked in blue tape)
Overall rating: 4/5 stars
Ease of application: Messy and difficult - ink was very runny and prone to smudging.
Durability: Very good
Ease of removal: Did not come off when rubbed with finger; hot soapy water and a bit of scrubbing took it off without leaving residue.
5. Name: Sharpie Paint Marker, Permanent Oil-Base, Medium tip, White (marked in red)
Overall rating: 4/5 stars
Ease of application: Easy. Consistent application. Paint goes on wet, so need to be careful not to smudge it.
Durability: Okay. Some fading occurred, but for the most part the treatment stuck on both the vertical line and custom design panes.
Ease of removal: Very easy - marker wiped off with finger, leaving no residue behind.
Notes: I applied this treatment in vertical lines, as well as in a custom pattern, to see if having more horizontal edges in the application made a difference (e.g., for wear caused by running water). Some fading was apparent on both panes with this treatment applied.
6. Name: Sharpie permanent marker, chisel tip (Black) (marked in yellow tape)
Overall rating: 1/5 stars
Ease of application: Easy, but ink did not dispense evenly and some areas were darker/more opaque.
Durability: Poor, faded within 6 months
Ease of removal: Medium— remaining ink did not wipe off with a finger, but came off with hot water and soap.
Notes: Definitely did not appear as conspicuous as the white ink, and would likely be less detectable by birds in most contexts.
Overall, some of the markers performed better than others. The markers with the greatest durability were 3. Dixon China Marker and 4. White Acrylic Paint Pen for Art. The latter was a bit tricky to apply when drawing vertical lines because the ink was prone to running or smudging, but with practice, this could be mitigated. Of course, mistakes can always be washed off and the application process restarted. An honourable mention goes to 5. Sharpie Paint Marker for being easier to apply (less ink issues), fairly durable, while also being very easy to remove.
Personally, I would probably recommend the oil-based Sharpie Paint Markers for most custom design applications, with the understanding that the designs may not last on the window for more than a year, and touchups may be needed. For custom designed installed by more skilled artists, the White Acrylic Paint Pen for Art provides more durability, but be careful of the ink running or smudging during the application process. For a simple treatment like vertical lines without a lot of edges or details, especially ones meant to last for a long period of time, I would probably recommend the Dixon China Marker.
While this test only looked at the white ink, I expect that versions of this product in other colours would perform similarly. When selecting a colour for a window treatment, it’s important to use visual markers that will provide contrast against the visual background so that birds will be able to notice it. In general, windows on buildings that appear dark should have light coloured markers. Glass railings and other uses where the glass appears lighter may do better with darker coloured visual markers. The single black marker tested here provided little contrast and poor durability.
Thank you to the sponsors who made this research project possible, and to you - the reader - for taking this knowledge into the world and using it to help save birds’ lives!