Tag Archives: cyanotype

Building a UV LED light box for cyanotype and lumen printing

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The cyanotype and lumen printing processes are two of the more frequently practised alternative photographic processes, because of their overall simplicity and the fact there is little-to-no need for equipment. Most people will do their exposures outside in the Sun initially, but if you want to work with these processes on a regular basis it can be frustrating to have ideas ready to try, but be delayed by lack of a sunny day. While it is still possible to expose on cloudy days, the length of time required to obtain a suitable image is greatly increased. Working with the sun it is also difficult to figure out predictable exposure times as the intensity varies according to the daily weather, time of day and time of year.

The solution is to switch to an artificial UV light source which can be used any time of day or year, whatever the weather, always giving the same exposure time. Historically though, UV exposure units have been relatively expensive to obtain, £100 or more. The ongoing developments in LED lighting technology though have now opened up new possibilities for constructing a custom UV light source for minimal cost. In particular it is possible to obtain 5m long strips holding 300 UV LEDs from online marketplaces such as eBay, for around £15 / $20 (search eBay for keywords “5M UV 5050 SMD 300LED“).

5M UV (395-405nm) waterproof 5050 SMD 300LED strip, powered by a 12 V @ 5 amp supply

5M UV (395-405nm) waterproof 5050 SMD 300LED strip, powered by a 12 V @ 5 amp supply

The 5M long 5050 LED strips are 1cm in diameter and can be cut every 3rd LED. If they are cut into groups of 15 LEDs, this will result in 20 LED strips, each 25 cm long. Arranged side by side, this allows for creating a light source that will evenly expose a 20 cm x 25 cm area which is practically perfect for both A4 and 8x10in paper sizes. If one didn’t mind lower intensity it would be possible to left a 1cm gap between strips producing a source suitable for 16x20in / A3 paper, at the cost of longer exposure times.

When cutting the LED strip up, it is important to cut exactly in the middle of the metal contacts between every 3rd LED, as it will shortly be necessary to solder wires onto the metal contacts. If using the waterproof coated LED strip, the rubbery coating will have to be removed from the contact pads after cutting, which is quite tedious and an argument in favour of the non-waterproof variants. With the strip cut into pieces, it is now time to connect them back together by soldering short (5-10 cm length) wires between the metal pads. While it is possible to wire them all together in series to form one long strip, this means the link wires will be carrying the full 5 amp current load and if any link goes bad it risks taking out the entire set of LEDs beyond it. A better bet is to wire them up in parallel, or perhaps grouped in a mesh giving multiple paths for the current, so the link wires only need handle a tiny current and there is redundancy. The important thing when soldering the link wires is to preserve the polarity between strips – ie connect positive to positive, and ground to ground.

All 20 strips with connecting wires soldered on. Mistakenly all 20 strips are in series. This was later resoldered to put them in parallel

All 20 strips with connecting wires soldered on. Mistakenly all 20 strips are in series. This was later resoldered to split them in 5 groups of 4 strips, each group in parallel, reducing current in the link wires to 1amp.

The vendors of the LED strips will typically also sell suitable power supplies. These mains powered units need to output 12 volts and be capable of supplying 5 amps to enable the LEDs to run at full brightness. Lower amperage PSUs will work, but the reduced LED intensity will obviously increase exposure times, so it is best to simply get the right specification of PSU from the start.

Mains PSU for the LED strip able to supply 12 volt at 5 amp

Mains PSU for the LED strip able to supply 12 volt at 5 amp

The power supply will likely have either a 2.5mm or 2.1mm plug, so a correspond matching socket needs to be purchased. While it is possible to just turn the device on/off at the wall, or by pulling the plug out, a better bet is to put a rocker switch inline with the positive power line between the plug socket and the LED strip. Again make sure the rocker switch is rated to carry 5 amps.

Power output is given by multiplying voltage by current, so 12 volt at 5 amps will produce 60 watts of power output. This is going to generate a reasonably large amount of heat and if something is not done about this, it will gradually degrade the LEDs shortening their lifetime. The obvious answer to this is to obtain a couple of 12 volt computer fans to fit in the case of the final light box. A fan that is approximately 4cm x 4cm in diameter will be ideal. They’re quite cheap so you might even consider using a pair of fans. The wires from the fan can be connected in parallel with the LED strips, since they’re conveniently driven from the same voltage. Do NOT connect them in series with the LEDs, as the 5 amp current draw of the LED circuit will kill the fans. Also be careful to get the positive/ground polarity right when connecting the fan, as reversing polarity will NOT make the fan run in reverse and likely kill the fan too.

12 volt computer fan, 4cm in diameter

12 volt computer fan, 4cm in diameter

The case for the light box will be made out of wood and comprise two pieces, a base which will hold the paper to be exposed and a slightly larger lid which will hold the LED panel. Both will have sides and be sized so that the base nests snugly inside the lid (or vica-verca). The top and bottom panels can both be cut from a sheet of 3mm plywood, the lid panel being 39×30.5cm and the base panel 36.5×25.5cm. These sizes are fairly arbitrary – the smaller simply needs to be about 2 inches larger than the size of paper to be exposed on each side. So for 8×10 paper, the smaller would want to be about 12×14 inches. For the larger lid, sides were cut from a length of 70x18mm timber, and nailed to the plywood panel. For the smaller base, sides were cut from a length of 36x10mm timber. In the timber sides of the lid, two 4x4cm holes were cut to hold the fans. Two holes were also drilled in the lid, one for the power supply plug socket and the other for the on/off rocker switch. When inserting the fans in the case, one should be oriented so that it sucks air into the case while the other should blow air out of the case, creating good airflow across the LED panel.

Light box lid showing the on/off rocker switch through the panel and power supply socket in the side

Light box lid showing the on/off rocker switch through the panel and power supply socket in the side

Close up of the lid, showing the computer fan inserted in the side to pull air across the LEDs for cooling.

The LED strip usually comes with a self-adhesive backing tape which is supposed to be able to stick the LEDs to most surfaces. This proved insufficiently sticky for me, so I applied super-glue instead. While the LED strips could be attached directly to the lid of the light box, it was thought preferable to attach them to a sheet of perspex or aluminium to allow the LED sheet to be separated from the case if needed. If using metal just be careful to avoid any short circuits with the link wires of the LED. Once the LEDs are attached, the sheet can be fixed to the inside of the lid with a couple of screws.

The larger lid, showing the metal plate with LED strips attached. At either end are cardboard shields to block UV light leakage through the fans.

The light box base

The smaller lightbox base, sized to be able to hold an 8×10 inch picture frame from a pound shop. Note a couple of screws sticking out of each side of the base, to prevent it sliding completely inside the lid when nested

When first turning it on, there was some UV light leakage through the cooling fans. Thus a couple of shields were cut from heavy duty cardboard and duct taped over the fan openings. With this in place there is no significant UV leakage from the light box, due to the closely nested lid and base. The UV LEDs are emitting at the end of the UVA spectrum, quite close to the start of the visible light spectrum, so the light is not a serious danger like UVB light would be, but it is none the less worth taking care to avoid accidental exposure.

In use the light box has proved to be intense enough to expose acceptable cyanotype images in as little as 5 minutes, and lumen images in anywhere from 10 minutes upwards depending on the visible effect desired. This is considerably faster than many commercially obtainable UV light sources that photographers have used in the past, which could take 15 to 30 minutes or even more. All together the cost of the complete box was probably around £45 – if you already have some parts in the shed such as plywood / timber pieces and a suitable power supply, then the price could be around £20-25. Either way, it will easily beat the cost of commercially produced light boxes and likely perform better too. The hardest part in construction is probably the soldering of the 50+ link wires between the LED strips. The case needs only minimal wood working skills – use of a saw and hammer. In summary creation of the light box is a very worthwhile use of time and money and will proof useful for years after.

An introduction to the Lumen printing process

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I don’t have space for a darkroom at home, and while there are still a number darkrooms across London that provide training and rental, this quickly gets expensive and lacks convenience due to travel time involved. As such I have an interest in traditional photographic techniques which can be performed under normal interior or exterior light conditions. Film development requires nothing more than a changing bag to transfer the film to the processing reel. The cyanotype process only needs limited darkness after coating the paper while it dries, thereafter the actual exposure takes place outside in direct sunlight or via a UV exposure unit. While the chemigram process could be done in a darkroom, it is most commonly done in daylight as image formation doesn’t rely on light, but rather interaction of the chemicals to write onto the paper.

Continuing with this theme, the time came to try out the Lumen printing process. Many people are familiar with the photogram technique. Objects are placed directly onto light sensitive paper, which is then exposed under a enlarger, typically forming silhouettes of the objects where they blocked the light source. The paper is then processed in developer and fixer following the normal black & white printing process. This of course requires use of a darkroom.

Those who have handled traditional black & white photographic paper may have noticed that when it is exposed to daylight it slowly changes colour. Normally this would be a disaster making the paper useless for further photographic use. The Lumen printing process though, takes advantage of this behaviour in combination with a photogram like technique. Objects are placed directly onto light sensitive paper, and it is exposed to a light source, but this time it is either sunlight or a UV exposure unit. Over the course of the exposure, which can last anywhere from 20 minutes to several hours, the photographic paper will gradually change colour forming a silhouette of the objects. Once the paper is exposed, it would NOT go anywhere near photographic developer as that would just turn the entire paper uniformly black. Instead it is placed straight into a fixer bath, followed by an archival wash

The image initially visible after exposure can be quite intense, but this will sadly fade somewhat during the fix, and the colours will also typically shift in tone. The result is an image which is fairly low contrast with quite subtle tones. What is surprising is that despite the use of black and white paper, the image will actually exhibit significant colouration. This is markedly different from what is seen when creating photograms where the image is still strictly black and white and high contrast.

A simple lumen plrint made with planet cuttings. The image is fairly low contrast and mostly shows an outline of the plants.

A simple lumen plrint made with planet cuttings. The image is fairly low contrast and mostly shows an outline of the plants.

There are a variety of factors which will influence the colours obtained in a Lumen print. A non-exhaustive list would include

  • Type of paper – each paper has a unique chemical formulation in its light sensitive coating(s) and as a result will behave differently when exposed to UV light
  • Age/condition of paper – the chemical formulation of the light sensitive coating(s) may change and degrade over time, depending on the way in which it was stored, which will in turn alter how it reacts with UV light
  • Time of exposure – the paper may undergo several colour changes as it receives increasing amounts of UV light. For example, it might start white, then go yellow, then blue. So varying the length of exposure will alter what colour the final image has.
  • Opacity of the objects – objects which are partially transparent to UV light will allow a range of exposures across the paper. Since colour is dependant on the amount of UV light, partially transparent objects can result in a range of colours being visible in the image.
  • Water on the paper – any water that is in contact with paper during exposure can influence the colours formed. The water can be applied manually, or it can leach out of the object (eg fresh cut flowers/plants) on the paper in the heat of the light.
  • Type of light source – while direct sunlight and UV exposure units both produce UV light, the sun provides a much broader spectrum, so will have a different effect than narrow band UV lamps. The sun is also a much more diffuse source than a lamp just millimeters away from the paper.
  • Toning of paper – the initial image will change and fade significantly during fixing. By toning the paper before fixing, it is possible to retain more intensity in the image and/or alter the colouring.
A Lumen print exhibiting varying colour tones. The image is dark purple where the paper was fully exposed, pale pink where fully obscured from light, and a yellow/brown where moisture from the leaves affected the paper

A Lumen print exhibiting varying colour tones. The image is dark purple where the paper was fully exposed, pale pink where fully obscured from light, and a yellow/brown where moisture from the leaves affected the paper

While some objects are heavy enough to make good contact with the paper and resist movement on their own, with others it might be necessary to weigh things down with a sheet of glass. This is particularly needed when using flowers and other plant material to form the image. There are a variety of options for this task. Those with existing darkroom equipment may well have one or more contact printing frames. These are quite expensive to obtain even on eBay, so more economical options are to obtain some suitable sheets of glass from a local glazing supplier, or use a cheap photo frame. With the prevalence of pound / dollar stores, finding cheap photo frames is remarkably easy. Why spend £50 on one contact printing frame, when you can buy 50 photo frames for £1 each. Being able to expose many prints at the same time will dramatically improve productivity, so it makes sense to go cheap and obtain many frames. It also means you won’t care if they get damaged or broken during use

An 8x10" sized glass photo frame from a pound shop, to use for contact print

An 8×10″ sized glass photo frame from a pound shop, to use for contact printing

One important thing to note is that the photo frame should have quick release clips for the backing board, not tacks that require pliers to remove and a hammer to re-insert !

An 8x10" sized glass photo frame from a pound shop. The quick release clips allow easy changing of paper.

An 8×10″ sized glass photo frame from a pound shop. The quick release clips allow easy changing of paper.

To use them, open up the back place the objects onto the glass in the arrangement desired. Remember to flip the arrangement left-to-right at this stage, since you’re looking at the image from the back, not front. Then place a sheet of B&W photo paper on the object, so the emulsion side is in contact with the objects. Finally replace the photo frame back and secure the clips in place. There should now be good contact between the objects and paper to ensure they are held still and make good contact for crisp edges. The pressure also helps to squeeze fluids out of plants which can help with colouration of the print.

With the frame prepared, flip it over, place it in direct sunlight and leave it for a while. Over time the colour of the paper will change where it is exposed to the UV light. At a minimum 15-20 minutes will probably be needed, but don’t be afraid to leave the image exposing for hours. Given the length of time involved, it is worth preparing many frames and exposing them all at once. When the desired arbitrary amount of time has elapsed, disassemble the frame to remove the photo paper and place it into the fixer. As mentioned earlier, the intensity of the image will fade somewhat and the colours may also change significantly. Once an archival fix and wash is completed though, the image should be stable thereafter.

The cyanotype process is often said to be one of the simplest to photographic techniques to teach people, but it is clear that the Lumen process gives it a good run for its money. If preparing your own materials, cyanotype requires a little bit of care in mixing the right quantities of chemicals for coating the paper. The Lumen process requires no preparation of the paper – it is merely necessary to mix up fixer at the documented dilution factor. There is a slight burden on Lumen printing when it comes to disposing of the fixer, as it will become increasingly contaminated with silver as more sheets are fixed. Overall though it is a quite straightforward and satisfying process to work with. It is hard go go wrong, beyond exposing for too short a time, so even with no prior experience you’ll get some decent results.

 

Ultraviolet: World Record Cyanotype

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At the start of May, the Wellcome Collection organized a festival, On Light, exploring the relationship to light, which naturally included a number of events related to photography and photographic processes. I went along on Saturday 2nd for “Ultraviolet: World Record Cyanotype”, where Melanie King, Constanza Isaza and Andrés Pantoja were aiming to create the world’s largest ever cyanotype print covering approx 110 square meters (actual dimensions 7.5m x 15m). I took along my ZeroImage 2000 camera to document the event, first shooting a roll of Kodak Tri-X 400 black and white 120 roll film and then a roll of Fuji Superia 400 colour 120 roll film.

The cyanotype was to be created on fabric, consisting of a number of individual sheets sewn together beforehand to achieve the world record size. The sensitization of the fabric with cyanotype chemicals was performed the evening/night before in St John on Bethnal Green Church. This of course had to be done at night to avoid premature exposure, considering also the long time needed to dry the fabric properly before it could be packed into a black light proof bag for transport. Prior to working with the full sized fabric, a couple of small pieces (estimate about 1.5m x 1m) were used for testing exposure times. Two willing volunteers lay down on the test strips for about 20 minutes, which were then quickly washed. As well as serving as the test exposure, they were interesting demonstrations for the assembled crowd to witness & understand what was going to be done with the full sized fabric.

The test sheet was put through a couple of cold water washes to develop the cyanotype image and wash away remaining chemicals

The test sheet was put through a couple of cold water washes to develop the cyanotype image and wash away remaining chemicals

The results of the 20 minute test exposure showing the outline of a volunteer who lay down to form the image

The results of the 20 minute test exposure showing the outline of a volunteer who lay down to form the image

With the successful test out of the way, the organizers moved forwards to assemble a large group of willing volunteers to be the subjects of the full size record attempt. The general idea was for the volunteers to simply lie down on the fabric in a self-determined pose. In addition to that, there was a collection of random objects, predominantly circular, which were to be laid out on the fabric to give some contrasting shapes in the image. The fabric was swiftly unrolled in a courtyard off Malet Place, the subject & objects took their places and so the exposure had begun.

The courtyard was certainly not comfortable, but the volunteers had to remain still for 20 minutes none the less. If you didn't know what was happening you might think there had been an outbreak of a deadly virus

The courtyard was certainly not comfortable, but the volunteers had to remain still for 20 minutes none the less. If you didn’t know what was happening you might think there had been an outbreak of a deadly virus

At the end of their nap time, the subjects had to pick themselves up and collect the other random objects that were placed on the cyanotype. The places where they had been just showed a faint ghostly presence

At the end of their nap time, the subjects had to pick themselves up and collect the other random objects that were placed on the cyanotype. The places where they had been just showed a faint ghostly presence

Upon completion of the exposure, the fabric was quickly bundled up and transferred into the large water tubs for washing. This followed the same process as washing the test sheet, except that it took many more changes of the water to fully develop the classic cyanotype blue (& rinse off the chemicals) due to the immense size. After a lot of hard work by the organizers and their team of assistants though, the final result was ready to be revealed.

After washing the final developed cyanotype image was revealed to the world.

After washing the final developed cyanotype image was revealed to the world.

The ghostly impressions after exposure were transformed into dramatic figures after developing

The ghostly impressions after exposure were transformed into dramatic figures after developing

The sheer scale of the finished cyanotype was incredible to behold. The world record attempt was a dramatic success.

The sheer scale of the finished cyanotype was incredible to behold. The world record attempt was a dramatic success.

As can be seen from the images, the world record attempt was an unqualified success. The exposure was spot on, resulting in very dramatic high contrast outlines of the test subjects, even with the dull overcast day. The range of different poses the volunteers had chosen to hold were fascinating & entertaining at the same time. The only so called “problem” to come out of the day, was that of deciding what on earth to do with the finished cyanotype fabric. It would be a shame for it to remain in a bag for the rest of its life, but due to its size, there are obviously few locations / galleries which have the ability to display it. None the less it was recently announced that the fabric will be travelling to Spain to be displayed in the Revel-T festival this summer

The event was inspirational and left me with an enhanced passion for working with the cyanotype process. To anyone attempting to break this record though – don’t underestimate the amount of work involved in achieving something that on the surface sounds rather simple – nothing is easy at this scale, as the organizers and their assistants will attest.

The organizers and some of their assistants. From left to right, Hollie Quinn, Melanie Kathryn King, Francesca Polo, Constanza Isaza Martinez and Tres Peces Navegando.

The organizers and some of their assistants. From left to right, Hollie Quinn, Melanie Kathryn King, Francesca Polo, Constanza Isaza Martinez and Tres Peces Navegando.