A few decades ago, when I first started out, I believed sizing was about cutting the paper into the right size: I was very wrong. When a paper is “sized”, glue is used to bind the paper to control the absorption of liquids—the capillarity—in the fibres.
A paper towel is unsized and very absorbent since you are supposed to use it to wipe up spills. This is referred to as waterleaf. Fine art papers such as watercolour paper or printmaking paper are sized to give the painter a chance to work with the paint on the surface before it dries. The way the paper is sized will invariably affect the print.
Sizing helps keep the emulsion on the surface rather than soaking in and also makes the paper more sturdy. Without sizing the emulsion will penetrate deeper into the paper, and apart from using up more emulsion, the print may appear dull, and the emulsion may be set too deep in the fibres and not clear in the wash.
Sizing for vegans and carnivores
Gelatin made from animal hide or bones plus a hardener such as alum is often used to size papers (1) but there are also synthetic sizers, often AKD, and vegetarian options such as starch. Alkyl ketene dimer (AKD) is a synthetic size derived from fatty acids and is usually vegan, though in some cases not. Hahnemühle uses AKD and their papers are classed as ‘vegan’.
Internal and external sizing
Papers can be sized using internal sizing, external sizing or a combination of both. There are various exceptions but, in general, watercolour papers are externally sized to prevent water from absorbing too quickly, letting the artist work with paint on the surface before it sets. Sizing is done to improve the mechanical stability of the paper. In terms of alternative photographic processes, this is generally a good thing. Papers made for printmaking tend to be internally sized, to absorb liquid. This is good for intaglio printing, but in alternative photographic processes, it can cause the print to be dull.
Internal sizing: Internal sizing (also called engine sizing) is when sizing agents are added to the paper pulp as one of the “ingredients”. For cyanotypes, internal sizing with Aquapel or alkylketene dimerthe as well as alum-rosin sized papers seem to work well, but their archival quality has been questioned (2).
External sizing: External sizing (also called tub sizing, or surface sizing) is when the formed sheets are pulled through a sizing bath.
The term “hard sized” is when the papers are treated to have a high degree of water resistance and are often used for food packaging. According to Mike Ware surface sizing can cause botching in of the print especially if printing in platinum “Gelatin-sized papers must be avoided If the sensitizer contains a significant proportion of platinum, because gelatin can bind strongly to platinum(II) in aqueous solution, and the resulting protein (aminoacid) complex of platinum(II) is less readily reduced to platinum metal by the iron(II) photoproduct. This problem does not arise with palladium, which is more reactive.” (3)
Sizing may cause blotching
If your print turns out blotchy, external sizing may be the cause. Mike Ware explains how this happens: “Blotching can also be brought about by chemical treatment of the sheet after it is formed, i.e. by surface sizing, whether applied in the mill or subsequently by the user of the paper.”(3)
Oxidised starch, used for sizing can bind the iron(III) and diminish the efficiency of the sensitizer, shortening the exposure scale, thus causing staining.
“In general, no good purpose is served by starch-sizing a paper intended for siderotype processes. Papers internally sized with alum-rosin or alkyl ketene dimer (e.g. Aquapel) seem perfectly compatible with the processes.”(3)
Note: Sideortype processes include argyrotype, chrysotype, cyanotype, kallitype, platinotype, platinum prints and vandykes.
Which alternative photographic processes need sized papers?
So, does your paper need sizing or not? It depends on which process you are using. A few years ago we did a “Sizing survey” and you can see what other artists do. Take into consideration when it says “no need to size”, the artist may have used a paper that is already sized, so that’s why they have decided no extra sizing was needed.
Testing if the paper is sized
A quick, but not 100% accurate test, suggested to me by Robert Poole, to indicate if a paper is sized or not can be done by placing a drop of ink on the paper and see if it stays on the surface or soaks in. If it stays on the surface it is most likely sized, if it gets absorbed it is probably less sized.
How to size papers
Sizing enhances the paper’s resistance to buckling and allows for the print to “stay on the surface” which can increase both sharpness and contrast. External or added sizing can also prevent the effects of chemicals reacting badly with the buffering. Unsized papers can be sized using arrowroot starch, PVA (Poly Vinyl Acetate) or gelatin, but it is easier just to buy a sized paper from the start. If you find you need to size a paper this can be done. Here are a couple of ways
Method for sizing papers with gelatin:
- Dissolve 1 tablespoon of unflavored gelatin in 1 cup of warm water.
- Allow the mixture to cool slightly, ensuring it remains in liquid form.
- Apply the gelatin solution evenly to the paper using a brush or sponge.
- Hang the paper to dry completely.
Method for sizing papers with arrowroot:
- Mix 2 tablespoons of arrowroot powder with cold water to create a smooth paste.
- Heat the mixture over low heat until it thickens, stirring continuously to avoid lumps.
- Allow the arrowroot solution to cool to room temperature.
- Apply the arrowroot paste evenly to the paper surface using a brush or sponge.
- Let the paper dry completely.
Method for sizing papers using PVA:
- Dilute PVA adhesive with water in a 1:4 ratio, meaning one part PVA to four parts water. Adjust the ratio based on the desired level of sizing: more PVA will result in a stronger sizing effect.
- Mix the PVA solution thoroughly to ensure a consistent blend.
- Apply the PVA solution evenly to the paper surface using a brush or sponge. Ensure a uniform coat to control absorbency effectively.
- Allow the paper to dry completely. The PVA will create a transparent and flexible sizing layer on the paper.
Sizing for alternative photographic processes
Different processes may benefit from a specific sizing, here are a few examples, but please note there are many many ways of doing this!
- Carbon transfer prints work with gelatin sizing but do not bond with starch sizing. An addition by Don Nelson: – for carbon transfer printing, gelatin sizing will require hardening to prevent the gelatin from washing away during processing. Unlike other alt processes, gelatin sizing for carbon transfer is used to ensure that the pigmented gelatin image layer attaches firmly to the paper. Sizing gelatin for carbon transfer may also contain a small portion of albumen to assist in retaining the image.
- Cyanotypes work well with starch sizing.
- Gum bichromates or carbon printing, typically works with a polymer/colloid sizing such as gelatin, gum, or acrylic.
If you have any other recipes or insights, don’t hesitate to share them and we will add them to the list!
Further reading and references
- Dr Mike Ware, Chrysonomicon II – Practice, available to read for free: Chapter 2, ‘Choice and Coating of Paper, pp. 26-49 (2020)
- Dr Mike Ware, Cyanomicon, available to read for free: Chapter 6, ‘Paper Characteristics’, § 6.4.1, pp. 176-179 of the iBook ‘Cyanomicon’
- ‘Papermaking Additives Cause Degradation’ under ‘Technical Issues’ on Mike Ware’s website.
If you are curious to learn more, here are a few links to check out:
- Iowa University Libraries – a huge collection of links. Read them all and you have enough knowledge to get a degree in papermaking:
- Christina Z. Anderson’s book Cyanotype: The Blueprint in Contemporary Practice – Chris did extensive research on which papers work and which do not. If you do cyanotypes, read and save yourself many hours on wasted prints.
- Mike Ware’s publications – free to read. Note these are only relevant to siderotype processes, not gum and other colloidal processes:
Good luck printing!