Chlorophyll printing and pigments

Chlorophyll printing is a sustainable photographic process using plants and pigments to develop a print or a cameraless photogram. Almudena Romero shares her knowledge of the process.

Writer and photography / Almudena Romero

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Since the 1840s, artists have used organic techniques to produce photographs, sometimes using flowers, as is the case in anthotype printing, and sometimes by blocking or exposing plants to UV light. A lot can be learned about the beginning of organic photography on the paper Pictorial demonstrations of photosynthesis.

“To make a chlorophyll print we will let a leaf receive an extraordinary amount of sunlight so it changes some of its pigments from green to yellow.”

Most leaves have a variety of pigments that can absorb and release energy from a wide range of wavelengths. These are the chlorophyll, carotenoid and anthocyanin pigments.

Chlorophyll pigments, the green ones, absorb UV and visible light and reflect back green light. These are the main pigments active in photosynthesis and can convert light energy into chemical energy. However, they do not help to release any energy, so if the plant receives too much sunlight, only carotenoid pigments can intervene.

Carotenoid pigments absorb less of the UV light and more of the violet and blue-green light. They can reflect yellow, orange and sometimes red light to us. Carotenoids are present on plant leaves, but we often don’t see them as much because chlorophyll pigments are more abundant, therefore masking any other tone. Carotenoids play a crucial role when there is too much UV available.

When we leave a plant or a leaf in full sunlight it receives a huge amount of energy. It can damage the photosynthetic machinery. Carotenoid pigments can dissipate any excess as heat as they are able to convert chemical potential energy into vibrational energy. To keep a healthy UV diet and preserve the photosynthetic mechanism, the leaf changes its pigments and gets rid of the excess energy. Chlorophyll printing is based on forcing this pigment change. It is not about drying leaves or plants, which would result in brown, curly, and very fragile leaves instead of any print.

We must choose the right plant to produce a print. Some plants can easily cope with high levels of UV light without forcing any pigment change, such as palm plants, aloe vera, jade plants and snake plants. Other plants, will simply die before they manage to produce a pigment change such as Peace lilies and Monsteras. Some other plants have visible carotenoid pigments and don’t need to go through any change. We should avoid evergreen plants, variegatas, and climbing plants such as Devil’s Ivy.

I recommend leaves from Hosta, Colocasia and Alocasia plants. We might be able to produce a print in 6 hours with these plants. Aspidistra leaves are also very good for this process, however, it might take 1 to 3 weeks to get a print on an Aspidistra leaf. The majority of the plants from the Araceae family work very well, and generally speaking, green flat leaves from shadow tropical climates with no patterns would be your best choice.

Steps to make a chlorophyll print

1Choose an image for your chlorophyll print
We can choose an image from our phone or computer, but we will need to make some adjustments to get it ready for printing. There are free apps and computer programs to help us do this. We will first need to convert the photo into a black and white picture, then, slightly increase the contrast, and lastly flip it horizontally. Then we can print the image with a home printer.
The majority of home printers are inkjet printers. We should load inkjet printers with clear digital transfer film or OHP transparency film. Transfer or transparency film has micro ceramics that absorb the printer ink instead of letting it run down.
We will load the film on the printer placing the micro ceramics on the printing side. Just by touching the digital transfer film, we can tell where the micro ceramics are. One side of the film will feel stickier than the other. The sticky side is the one with the micro ceramics. If we choose to work with a laser printer, like a photocopier, we can simply use standard acetates with no micro ceramics.

2Check the weather
Once we have the right plant and the right acetate we must check the weather as we can only start the process on a sunny summer day.
We need to cut a leaf from a plant, place it in a frame and let it record an image by forcing a pigment change before it dries. If we start the exposure on a cloudy day, no pigment change will happen.
We must do the cutting of the leaf at about 11 am. It is good to start the process with the highest amount of UV light (around noon) as this will help the pigment change while the leaf is still fresh.

3Load the frame
We should place the inked side of the acetate in contact with the leaf. The layer order from bottom to top is: backboard, leaf, acetate and lastly glass.
It is important that we use many clamps and pegs to hold the acetate and the leaf against each other very tightly. It will take us several hours to make a print, so our materials must not be loose inside the picture frame. The amount of pressure applied to hold the acetate and the leaf together will determine how sharp or blurry the final print is. The more pressure the sharper the print.
We can also increase the amount of pressure in our printing frame by placing some paper or fabric on the back of the leaf. This will help to accommodate the volume from the veins of the leaf.

4Expose the print
On bright summer days, hostas and alocasias can record an image in hours. Aspidistras usually take several days or weeks. The clear areas of the acetate, where there is no ink, will look yellow on the plant leaf and the dark areas of the acetate (the dark tones of your image) will remain green. We can judge by eye if the printing process is complete.

5Fix and wax the image
Chlorophyll prints are very delicate since the image is directly recorded on a plant leaf. To fix the image we should:
First: Immerse the leaf in a bath of boiling water with a pinch of baking soda for 5 min. The alkaline boiling water will break the cell structure of the leaf.
Second: Boil a mix of 10 grams of copper sulfate, with 300 mL of glycerin and one litre of distilled water. Mix these 3 ingredients before boiling. Once boiled, let it cool, and then immerse the leaf in the bath for 10 minutes. The copper bath will replace the magnesium in the chlorophyll with a copper ion. This Copper chlorophyll complex is not photosensitive, and so will keep the green areas of the leaf green.
Third: Take the leaf out of the bath and wipe off any remaining copper sulfate.
Fourth: Wax the leaf or varnish it to prevent it from oxidizing. Renaissance wax has microcrystals that filter out UV light. Gum sandarac varnish also works very well and other less organic varnishes with UV filters. Some people prefer to immerse the leaves in epoxy resin blocks, but epoxy resins are very aggressive to the environment, clashing with the organic nature of this process.

These are the basic steps of the process.

 

Almudena Romero (b. in Madrid in 1986) is a visual artist based in London working with a wide range of photographic processes. Her work promotes a broad understanding of photographic forms and materials and has been featured in BBC Four, BBC Two, FOAM Magazine, Photomonitor, Radio France Internationale, TimeOut, DUST magazine, EXTRA magazine (FOMU, Foto Museum) and other media. She is a Fellow of the Higher Education Academy and has delivered courses, lectures and artist talks at universities and museums internationally. More of her work can be found at Almudena Romero’s website.