Japanese print of mountains and coastline

Dōmoto Inshō, Cherry Blossoms in Rain at Arashiyama, 1928, Los Angeles County Museum of Art, Gift of Mr. and Mrs. Felix Juda, © Dōmoto Inshō , photo © Museum Associates / LACMA

Removing Stains From a Japanese Print Using Gellan Gum

August 27, 2021
Madison Brockman, Andrew W. Mellon Fellow in Paper Conservation

This summer, LACMA launched the YouTube series ART + WORK, which shows the care that museum conservators put into preserving a wide range of artworks from our permanent collection. 

In this video Madison Brockman, former Andrew W. Mellon Fellow in Paper Conservation and now Assistant Paper Conservator, reduces the discoloration of a Japanese print using a gellan gum slab. 

Below Madison discusses this unique process for bathing a print in more detail. 

Tell me about the print you are working on today. 

This is a Japanese print, made with several colors of printing ink, that is part of the permanent collection at LACMA. I'm treating it today in preparation for an exhibition titled Sam Francis in Japan: Emptiness Overflowing, which is forthcoming here at LACMA. This object has quite a bit of discoloration, which you can see in some closeups as almost freckle-like spots called foxing. This is quite a common occurrence with paper collections and can sometimes be very difficult to reduce or remove. It's very distracting with this print in particular, especially in the negative spaces of the image where the foxing is very visible. 

Foxing is typically caused by fungal present in the paper, but it can also be from metallic inclusions, especially iron. Both catalyze the auto-oxidation of cellulose, meaning that they help speed along the normal degradation of the plant fibers that paper is made of. This occurs locally, in discrete spots where a metallic inclusion or fungal growth is located, so you start seeing little spots of yellow to brown discoloration in those areas.

How do paper conservators treat discoloration? 

Most of the time paper conservators will treat objects with water—we call this aqueous treatment—to help wash away acidic degradation products that cause discoloration. Aqueous treatment can be delivered in many forms, including full immersion into a bath, a localized application of water on a vacuum suction table to help pull it through the paper, or more recent innovations like bathing on rigid polysaccharide gels (which includes gellan gum), which you'll see in this treatment. Bathing a work on paper may sound surprising or scary, but it’s a routine treatment in paper conservation that helps extend the life of an artwork by reducing acidity and restoring some flexibility to the sheet. Think of it as a much-needed spa day!

Why did you decide to treat this print using a gellan gum slab? 

I'm treating this specific object by bathing it on a gellan gum slab rather than using a full immersion bath because the object is a little bit fragile. It is printed with several colors of ink, and also has some blind embossing in the design image, so the print has a very delicate surface that we don't want to disturb by immersing the object in too much water. Bathing on the gellum gum slab will be a nice way of getting effective aqueous cleaning while making sure that the object is physically stable. 

There are quite a few steps before the object is actually bathed. Can you share a little about those steps? 

Before any treatment, I examine the print’s surface with a light source held at a sharp angle, which we call raking light. This angle of light can eliminate the surface texture of the paper and can alert me to any special characteristics like the blind embossing or any condition issues that I might need to keep in mind while treating this object. Examination is a very important part of any kind of conservation specialty. Conservators do a lot of close looking at each individual object, especially before we do any kind of treatment. 

After examination I need to ensure the different printing inks will be stable during treatment, namely that they are not water-soluble. I do this by applying a very small droplet of water in an inconspicuous location on each of the different colors, and after a while lightly press a small piece of clean cotton blotter on the testing area. If the blotter comes up clean, the ink should be safe for aqueous treatment; highly water soluble inks will be deposited on the blotter, alerting you to the fact that the object cannot be treated with water and alternatives must be considered. 

After testing, I do some light surface cleaning to clean away any superficial dust or debris that settled on the print over time. This is especially important before doing any kind of aqueous treatment because the introduction of water will swell the paper and any dirt or debris on its surface will become deeply embedded and very difficult to remove later on. So paper conservators always do some light surface cleaning before introducing any kind of moisture. I'm using a cosmetic sponge, made from polyurethane, which just gently picks up any dust or debris on the surface without disturbing the paper fibers below. 

What is the solution that the print is being bathed in? 

For this treatment I'm not just using plain water, although that can also help to reduce discoloration. Instead I'm using a targeted cleaning solution, which increases the cleaning efficiency beyond what water alone can accomplish. I’m using a one percent (weight to volume) sodium citrate solution, which acts as a pH buffer and a chelator, which helps make insoluble degradation products in the paper more water soluble so they can be removed in the bath. I’m also adding a very small amount of calcium acetate, which helps form the gel matrix of the gellan gum slab itself. Without the calcium acetate, the liquid gel would not set up very well and the slab would not be fully solid.

For the gellan gum, I use a one percent concentrate for washing because it allows lots of water to be present and to deliver that cleaning solution to the paper. This means that of the gel slab, one percent is gellan gum and 99 percent is water, even though it's a rigid structure! That's pretty amazing. The gellan is insoluble in water and must be heated to fully solubilize it or get it into liquid form, then it solidifies as it cools. If you have ever prepared Jell-O at home, the process is the same, although the polymers are very different (Jell-O is gelatin, a protein, whereas gellan gum is a polysaccharide, or carbohydrate).

How long does this treatment take? 

The bathing time for each individual object varies, but for this particular print, I'm going to bathe it for about an hour with the citrate solution. We just have to ensure that the cleaning solution in the gel has plenty of time to make its way into and out of the paper to help reduce the foxing spots and overall discoloration. A lot of this is just based on practice and experience, knowing when a bath is done.

After an hour, I'll remove the print from the citrate gel slab and then bathe it for another hour on a second gel slab that doesn't have the citrate solution, just water. This will rinse out citrate solution from the print and ensure that it's not remaining there for the long term.