While there are several ways of sizing art paper and I've tried many, and most of them with success. My most common method uses gelatin hardened with glyoxal. I've tried several other sizing techniques but keep coming back to this one.
I'm basing this on two sources, both highly recommended:
- The Carbon Print: The History, Theory, and Practice of Carbon Transfer Printing. Sandy King & John Lockhart (2017)
- The Book of Alternative Photographic Processes (3rd Ed.) Christopher James ISBN 978-285-09831-7 (2016)
Gelatin As I have said in other blogs gelatin is primarily a protein - it is very safe and is used widely in the food industry - it's fed to kids as jelly. So it is about as safe as it gets. So no Safety Data Sheet is needed. Though I wouldn't mix my photographic gelatin with the kitchen variety, just in case.
Glyoxal, though, is poisonous and needs to be treated with a little respect - here is the Glyoxal Safety Data Sheet that came with mine. If you search on the internet you will see that it is used in disinfectants and cleaning agents in hospitals - so, while it is poisonous, it is not that deadly. Here is a useful page on Health and Safety of glyoxal. Wear a mask at all times and do not get it on your skin, wear gloves.
I use 240 Bloom gelatin, which I got off the internet, and from which I will make a 5% m/v solution. When I make up the gelatin I prefer to make up just enough to size the paper I need - often three or sheets at a time. My favourite paper, Saunders Waterford, I buy in an Imperial sizes; 760mm x 560mm. I have written my own 'ready reckoner' (an Excel spreadsheet I carry on my phone) and this paper needs 25ml for two coats on one sheet.
I will do the calculations in these notes for 1,000ml (1 litre), but the proportions can be scaled down. 5% m/v requires 50g of gelatin
For thinner paper I often size both sides because it greatly reduces curling.
It is recommended that before you add all the water you start by adding the gelatin to a smaller amount and allow it to bloom for 20 minutes.
Ingredients for 1,000ml
- 50g Gelatin
- 1,000ml de-ionised water - divided into 300ml then 700ml
Note for four sheets of 760mm x 560mm you need: 4.7g of gelatin in 94ml de-ionised water
- Double boiler
- Kitchen thermometer
- Measuring jug
- Weighing scales
- 760mm x 560mm Saunders Waterford paper (normally 300gsm HP)
- 40mm foam brush
Two Stage Process
I do this in two stages:
- Coating with gelatin
- Hardening with glyoxal
Here is my technique: for the first stage, coating with gelatin
- The Gelatin Bloom Add the full 50g of gelatin to 300ml of cold de-ionised water and leave to bloom for 20 minutes. You will see the gelatin expand and soak up all the water. Then add the remaining 700ml of water and stir in before heating.
- Heating the gelatin I have used a simple double boiler technique, which involves a pan of water on the kitchen stove, with a suitable container that holds the gelatin solution without spilling. The gelatin will dissolve completely at 50°C and the trick is to measure the temperature using a kitchen thermometer. I heat the pan and never let the water boil and slowly watch the temperature rise to 50°C. The trick is to keep it at that temperature while you coat. When making jelly to eat I use the microwave to great effect, and experimenting I have found I can get the gelatin to 50°C much quicker and more easily using this technique.
- First Coat I prefer not to pour out the gelatin for sizing, instead I use a foam brush (40mm for a large sheet of paper), which I make sure is damp, but not dripping, before first use. I like to dip the brush in the liquid gelatin and paint quickly but not so fast as to cause bubbles. Immediately after coating I hang the sheet up and give a first coat to all the other sheets, before returning to the first sheet and start sizing all over again.
- Second Coat I don't wait for the first coat to dry - the gelatin will set quickly and you can do the second coat almost immediately. It can be a little difficult to see what has been coated and what area has not had a second coat so I set up several lights around the coating table as well as the overhead light and look for reflections from the wet areas to guide me.
- Drying The papers then all get hung up to dry - I normally leave them for a day. Though the glyoxal can be applied before drying is complete
Glyoxal for Hardening Gelatin Size (0.6% v/v)
I always use a full face mask with filters when using glyoxal. I buy my glyoxal on the internet and it comes in small bottles at 40% v/v and dilute it down.
I have built myself a simple dipping tray for the glyoxal solution. I used a trough fro flowers that is longer than the 560mm width of the paper. Into this I put in a piece of plastic guttering that fits snuggly into the trough - they are not glued. I cut the gutter myself and added the end-caps. The glyoxal is poured into the gutter and the paper with the two coats of gelatin is 'rolled' through with the gelatin surface on the outside.
After coating I pour the glyoxal into a clearly marked bottle, which I use again - topping up as required.
Ingredients for 1,000ml
- 15ml 40% v/v Glyoxal
- 1,000ml de-ionised water
- 0.3g Sodium hydrogen carbonate (Bicarbonate of soda) - this keeps the solution alkaline, which in turn promotes the crosslinking that hardens the gelatin
- Measuring jug
- Weighing scales
- Home-made dipping tray for 760mm x 560mm paper
- Rubber gloves
- Full face mask
Here is my technique for the second stage, hardening with glyoxal:
- The Glyoxal Solution A litre of the glyoxal solution fills the gutter to the right level. No special mixing is need, which I do in a 2 litre plastic bottle - I shake it to ensure the sodium hydrogen carbonate is dissolved.
- Dipping Tray and Glyoxal Solution The design is very easy, it just fits together. Then pour in 1,000ml of the glyoxal solution
- Glyoxalate the Paper With the gelatin side outward and holding each end of the paper, start with one end of the paper fully submerged in the glyoxal solution. Then move the entire paper through the solution by feeding one end in while you pull the other end out. Only one pass of the paper is need, but attention is needed to make sure that the at any one moment the paper is fully submerged
- Hang the paper to dry Immediately the paper has been fully wetted along its entire length hang it up to dry. Leave hanging for at least 24 hours
- Store the paper Once dry, mark the paper with: paper type and weight, date of gelatin coating and date of glyoxalation
- While this is straightforward, this two-stage process is time consuming and does use a lot of glyoxal solution - I should explore a single-stage process and combine the glyoxal with the gelatin in the first coat