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Carbon Printing and Tissue
Dick Sullivan on Carbon Printing “Like baking bread, it’s a busy process and it can take some time”
I love this quote because on the surface it sounds off the cuff, but really, what exactly is ‘some time’? The process of making carbon tissue of or carbon printing is time consuming and labour intensive and after a few months of unsuccessful carbon printing, I have had to go back to basics. Re-evaluating each of the steps involved and analysing each process is starting to reward me with better results.
Carbon printing is challenging and certainly there is no quick fix. There is not much literature detailing the process and what there is dates back to the 19th and 20th century. Over the last few decades, a few key authorities (Sandy King, John Lockhart and Dick Sullivan) have produced some excellent manuals explaining the process in modern day language.
An added complication to the process is that of making the carbon tissue. Much of the knowledge of the process of making carbon tissue has died out and commercial carbon tissue production ceased in the 1990s. In the 2000s Bostick & Sullivan began producing carbon tissue but have since stopped production and as at this time (2019), it is not possible to buy carbon tissue. This leaves the carbon printer with no alternative other than to make their own carbon tissue.
Luckily, I am under the guidance of some experienced printers who have learnt from experts before them and who are generous enough to pass on their knowledge to me. Hopefully I will be successful in my endeavours.
A brief description of what a carbon print is – and isn’t.
In 1826 Joseph Nicéphore Niépce successfully recorded the first image. Captured rather crudely over several hours the image was recorded on a plate of pewter which was coated with bitumen. The bitumen was light sensitive. The areas exposed to sunlight hardened and the areas that received less or no sunlight remained soft. When the plate was washed, the hardened bitumen was unaffected. The soft bitumen washed away thereby creating the image.
Although the process and materials are different for a carbon print, the concept is similar to that first image recorded back in 1826.
Carbon prints are photographic images recorded using pigment suspended in a gelatin binder. The image density (lightness and darkness) is created by the thickness of the carbon. Thicker areas are darker. Thinner areas are lighter. The image can also be processed to have a relief affect.
The main ingredient of the carbon print is known as lamp black - basically, soot. It is made up of fine particles similar to cigarette smoke. One of the prized features of a carbon print is that it has proven to be highly archival and fade resistant. A carbon print will never fade.
Carbon prints were generally monotone although it is possible to make tri-colour carbon prints which are dazzling, unique and highly collectable.
The term “pigmente prints” was coined in the early 1900s for the carbon prints produced by Josef Sudek. The “pigment prints” of today, printed on an ink jet printer using carbon based inks are not considered by collectors to be true pigment prints.
The Process of Making Carbon Tissue
My intent here is not to discuss in detail the making of the carbon tissue but rather some of the challenges and how to overcome them. I hope the reader understands that I am a novice, having only been introduced to carbon printing in 2018. My hope is that by sharing my findings, perhaps it will help others who are interested in trying this method of alternative printing.
1. Making the carbon gelatin which is required for the carbon tissue
A major challenge has been the moisture content of the carbon gelatin. Standalone gelatin contains 8-13% moisture. The recipe for the carbon gelatin includes glycerine. My understanding was that the glycerine was for pliability only. However, the glycerine also assists with holding the moisture within the gelatin. Given that I’m working in a sub-tropical climate, where humidity is generally above 50%, I feel that I can safely reduce, or even remove, the glycerine from my recipe.
Another learning curve has been how much pigment to use. The recommended ratio of ink to carbon gelatin is 20ml to 1 litre. The aesthetic achieved from this recommendation is a personal one. This ratio produces a sepia print.
As I am after a true black I have experimented with higher concentrations of pigment and run densitometry tests. Despite the test results the prints still prints as sepia. I have now switched to lamp black and am achieving a blacker print. Again the ratio of powder to carbon gelatin is a factor as is, I am discovering, the substrate.
2. Making the carbon tissue – the biggest challenge of all!
I did not fully appreciate how different environments can affect the carbon tissue. I have wasted considerable time, effort and ingredients not understanding the melting and setting points of gelatin.
Once the carbon gelatin has been poured onto its temporary support it needs to dry. This is a key element to the process. Without dry gelatin, everything including the negative and mylar will stick to the gelatin and pull away when separated from the support.
When learning to make carbon gelatin and tissue, I was working in a studio in Victoria in the middle of winter. The temperature inside was 20°C (with heating), relative humidity 47%. Outside it was snowing! When I was instructed to leave the tissue to dry (and set) overnight, I didn’t give it another thought.
Climatically, Queensland could not be more different. Temperatures inside are 22°-25°C (with air conditioning). Relative humidity 60-70%. Outside temperatures are in the high 30s.
And so when I left my tissue to dry (and set) overnight, albeit in an air conditioned room (at 22°C) it wasn’t actually drying completely.
I had believed it was dry. That was until a good friend showed me his carbon tissue. It did not have any tack (stickiness) at all.
Burying my head in literature, I have established these vital numbers:
· Gelatin begins to soften at around 20°C (worth remembering)
· The melting point of gelatin is in the mid 40s.
· Working environment (for pouring) of 18°C-22°C is recommended
· Gelatin sets at around 15°C and needs to be kept at refrigeration temperatures (5°C) for at least 6-10 hours before solidifying
· Once set, you can freeze the carbon tissue at anything between -15 and -31°C.
Each practitioner needs to work out their own way of achieving each of these milestones. Personally I am using a variety of equipment which includes an air conditioner, a dehumidifier, a refrigerator, a freezer and most recently a wine cooler(!). I am most excited about the wine cooler as it has a temperature range of 5°C-20°C. Going forward I have far more control over my tissue.
Drying the tissue
In my quest to find the reason for my gelatin not drying, I considered that it may have had something to do with the bloom. Most literature recommends using 200 – 250 bloom for photographic practises. Some of the carbon gelatin manufactured in the 1990s was made with 130-150 bloom. I now understand that bloom is determined at the point of extraction (ie when the materials - skins and bones – are washed). The first extraction produces a superior product compared to subsequent extractions. The first extraction has a higher viscosity and higher gel strength. Typically the process entails 3-6 extractions, with each extraction requiring higher water temperatures which reduces the gel strength.
Gelatin is made up of over 50% carbon. Gelatin contains 6.8% hydrogen and 25% oxygen. The water content is negligible and so I do not believe that the bloom rating bears any relation to the moisture content.
The bloom content does however bear a relation to the gel strength. This could be a consideration when determining how well the image will adhere to a difficult substrate. A print could be made with a gelatin of a higher rating if the substrate is going to prove to be a difficult one (for the print to adhere to). However, it would be far more prudent to not rely on bloom strength for longevity but rather to make the print and employ the traditional techniques of ensuring the print's archival qualities.
How much to pour
Another control which I’ve had to master is the quantity of gelatin to pour onto my support paper.
According to The Carbon Print manual (by master printer Sandy King) the amount of carbon gelatin required for a 1mm wet depth of carbon gelatin in relation to the size of paper which you are coating is:
Width (cm) x length (cm) x 0.1(cm) = required amount in ml
I have found this formula to be very accurate and have had great results.
When pouring the carbon gelatin onto the support it is crucial that the surface is 100% level. If the surface is uneven the gelatin settles at different thicknesses resulting in a print with some odd looking tonal contrasts.
To achieve this 100% level surface I have sourced a sheet of steel from a local steel manufacturer. I lay this on my counter and together with a spirit level and some blu-tac (or putty) I set about modifying the level of the sheet of steel. When I’m sure that the sheet of steel is 100%, only then do I begin my pour.
A note here. My steel is beginning to rust and so perhaps a sheet of metal would be preferable.
How to pour
I lay my support paper on the steel. I have, ahead of time, marked out a border on the paper which indicates the boundary area for the gelatin. Using 1mm thick magnetic tape (cut to size), I make a bounding wall for the pour. Note that the magnetic tape is the same thickness as the gelatin pour is going to be (according to the above calculation).
There are two ways of pouring and spreading the gelatin. One method is to pour into the middle of the paper and use your fingers to spread the gelatin to the edges. The other is to use a rod. I don’t think that there is a right or wrong way and I’ve tried both. I’ve been very successful using the rod, although it is apparently only necessary for larger sheets. I am making small sheets, cut to the size of my final support, and I have found that the rod method provides a more uniform layer than when I use my fingers.
I pour the gelatin onto the support, starting in the middle and gradually making concentric circles. It spreads slowly, and given that the base is level, it does not run. Resting the rod on the magnetic strips, (the rod is slightly wider than the boundary ‘walls’), I gently drag the gelatin, first one way then the other. Generally no further dragging is required. The gelatin quickly settles and levels out.
Going back to the analogy of baking bread, I now understand what Dick Sullivan means by saying ‘it can take some time’.The level of detail involved in making carbon tissue and in making carbon prints, the exacting techniques and the patience required need true dedication. However the resulting print which has qualities of tone and texture are unlike any of the other alternative printing process. It is for this reason that the effort taken to achieve the final result will be worthwhile.