Plexiglass with cyanotype: contact frame, thickness and UV light
Cyanotype is one of the most beloved alternative photographic printing techniques. With only two chemicals – ferric ammonium citrate and potassium ferricyanide – and a dose of UV light, you can create the characteristic deep blue prints.
At Cyanoprints, we help you get the most out of this process. In this article, you’ll learn how to use plexiglass sheets for cyanotype, how thickness affects exposure time, and what kind of artistic effects you can achieve.
Plexiglass is mainly used in cyanotype as a contact plate : it presses a plant, object or negative surface against the coated paper or textile during UV exposure. Direct cyanotype coating on untreated plexiglass is less reliable, because the smooth, non-absorbent surface barely holds the emulsion. The correct thickness, clarity and UV transmittance of the contact plate do have a major influence on sharpness and exposure time.
Why use a contact plate?
- It prevents leaves or negatives from shifting.
- It improves contact and therefore sharpness.
- It protects a transparent negative against wind and warping.
- It makes it possible to move a complete composition safely.
What thickness works?
For small and medium prints, a relatively thin, flat plate is often sufficient. A thicker plate is stiffer and bends less, but weighs more and, depending on the material, can absorb slightly more UV. The ideal choice therefore depends on size and support. For a large plate, use several clamps or a contact frame so that the center does not come loose.
Does every plexiglass transmit UV?
No. Transparent to visible light does not automatically mean transparent to all UV wavelengths. Some plates are specifically made to block UV. Protective film, coatings, color and material type can delay exposure. Test a new plate next to a known glass plate or without a cover plate, with the same paper and the same UV source.
This is how you test the UV permeability
- Coat one strip of paper evenly and let it dry.
- Cover half with the plexiglass and leave the other half alone under the same composition or negative.
- Expose both parts at the same time.
- Rinse and let dry.
- If the part under plexiglass is clearly paler, extend the time or choose another plate.
Use the method from the guide on cyanotype exposure time to accurately record the new time.
Plexiglass or glass?
| Property | Plexiglass | Glass |
|---|---|---|
| Weight | Light | Heavier |
| Risk of breakage | Low, but can crack or scratch | Can break and create sharp edges |
| Rigidity | Depends on thickness | Often high at the same practical size |
| UV transmission | Highly dependent on type and coating | Depends on glass type and thickness |
| Maintenance | More prone to scratching | Easier to keep scratch-free |
This is how you build a simple contact setup
- Place a flat, sturdy base plate.
- Place the dry, coated paper layer side up.
- Place the object or negative on top.
- Remove protective film from both sides of the plexiglass.
- Place the plate cleanly and carefully on the composition.
- Clamp evenly all around without forcing fragile plexiglass.
Improve sharpness
Use a negative without curls and ensure that the paper and plate are dust-free. A single dust particle can become visible on a fine negative. Thick plants deliberately give softer edges; pre-press them when you want a more graphic result. For a large size, check whether the plate in the center actually makes contact.
Common mistakes
- Leave the protective film in place: film may be cloudy or filter UV more strongly.
- Use UV-resistant plate: This will make the time required much longer or hardly create an image.
- Too few clamps: Loss of contact causes blurred parts.
- Scratches and dirt: these can appear as unexpected marks in the print.
- Continue using the same time: another plate requires a new test.
Can you print directly on plexiglass?
Experimental artists sometimes use a special primer, gelatin, or other binding layer to hold cyanotype chemistry on a non-absorbent surface. That is a different, less predictable process than a classic cyanotype on paper. Test adhesion, rinse resistance and aging extensively; do not use an unprocessed plate as a guarantee for a durable print.
For the print itself, suitable cyanotype paper remains the most reliable basis. Also view the complete paper selection .
