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13 Aug 2021 / by Marta García Celma

Anatomy of a Photograph: Inside the Conservation Lab with Marta García Celma

A woman wearing a face mask and gloves bends over and looks intently at a large photograph on a table. Both hands are on the photograph, as if she is adjusting its positioning.

Conservator Marta García Celma readies a photograph for framing. Photo: Lok Cheng

When was the last time you held a physical photograph in your hands? In an age when almost anyone can instantly make and share an image on a mobile phone, it's easy to stop on the surface of a photograph: dismiss it with a cursory glance or a swipe of the finger, deposit it into the short memory of our media-saturated world. But underneath the surface of a photograph—and most especially a physical one—there is another story constantly unfolding. Each layer, scratch, fold, or fade offers clues about where a photograph has been and where it's going.

M+ Photography Conservator Marta García Celma gets up close with some of the photographs in our collections, zooming in on the surprising processes at work within this seemingly still object and highlighting the role that everyone can play in preserving this most democratic aspect of our shared visual culture.

In comparison to other media, photo conservation is still a relatively young field. What is it about the anatomy of a photograph that presents special challenges for conservation?

An important thing to remember is that not all photographs are made equally. Actually, they vary a lot! A lot of people think of a photograph as something on paper, and for many years, the person caring for photographs in a museum has been the paper conservator. But what do you do when you have photographs on glass, plastic, textile, metal, or ceramic? Or when the image is made by silver, dyes, pigments, or even ketchup?

Luckily, in the last twenty years, photography has been increasingly recognised as an independent fine art medium requiring specialised care. And while not many institutions in the world have a specialised photo conservator on its team, M+ has made space for one!

Monochrome photograph showing a white bottle's food label, which shows 'Free Choice 70% LESS FAT' on top, a barcode on the right, and the expiry date '07.97' at the bottom.

In Huang Yong Ping's Best Before 1 July, 1997 series, string and sealing wax are affixed to the gelatin silver print. © Huang Yong Ping; M+ Sigg Collection, Hong Kong. By donation

It is true that most of the physical photographs in our collections are paper-based, and while there are small differences between older and more contemporary ones, the structural anatomy of a photograph is often the same.

First, we encounter a support layer made of paper fibres and sometimes coatings. Older photographs have an additional baryta layer—a white layer of barium sulfate—which creates the background of the print. (This is simulated in digital prints with a white-pigmented layer.) On top of those are the image-making compounds, which might be silver halides or dye couplers suspended in gelatin, or pigments and dyes deposited on a liquid surface.

A photograph might look like a simple object, but when you look under a microscope, a new world opens!

Five long photographs side-by-side, each showing a different material in close up. From the left, the first is silver in colour with fine white dots; the second is blurry shades of magenta and yellow; the third shows dense dark grey, cyan, and magenta dots on a white background; the fourth shows dark lines formed of dense black dots; the fifth shows an evenly spaced hexagonal pattern of black, cyan, magenta, yellow, and green dots.

Under the microscope, photographs have a life and shape of their own. Shown here (left to right) are gelatin silver, chromogenic, two variations of inkjet, and electrophotography prints

How do your concerns vary according to the type of photograph?

When we work with a photograph, it’s imperative to identify what type of print we have, as each type of photograph will react differently to the same environmental agents: temperature, humidity, light and pollutants.

Photograph showing a silver material textured with fine white dots in close-up. There is a magnification scale in the bottom left corner labelled ‘0.5mm’. Along the bottom is the label ‘Silver gelatine print on matte paper’.

In gelatin silver prints, the primary image-making compound is silver nitrate, secured in a base coat of gelatin

The well-known black-and-white prints—gelatin silver prints—have a tendency towards yellowing with light and air, and then at some point, there can be oxidation of the silver. This is when the silver particles break and charge to the top, producing what we call silver mirroring, where if you look at the photograph and move, the dark areas reflect like a little mirror. While some may see it as deterioration, you cannot fake oxidation, so at the same time it’s proof of age.

Monochrome photograph of a man speaking and gesturing in front of written posters that are being held up by a different young man.

Many photographic works from the 1950s–1970s in the M+ Collections, such as Fan Ho’s Missionary (1960), are gelatin silver prints. © Fan Ho

Chromogenic prints, the traditional colour photographs popular until the early 2000s, will fade when exposed to heat and light. I am sure many of us have encountered colour photographs in which the whole scene looks magenta—well, that is an example of severe fading on chromogenic prints.

The reason these photographs have a high tendency to fade, even in the dark, is because an agent with high impact on them is temperature. When the temperature is high, or when constant fluctuations of temperature take place, the particles that make this print start ‘dancing around’.

Photograph showing a blurry magenta, yellow, and green material in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Chromogenic print on glossy paper’.

Chromogenic prints have three layers of dye couplers encased in gelatin, reactive to cyan, yellow, and magenta, respectively

In a way, it’s like food. If you leave something outside of your fridge, in one or two days, it’s probably off and mouldy, because the temperature and humidity are promoting the molecules to move and let more organic compounds come in and interfere. However, if you put this food in the fridge, nothing happens. The molecules are stuck; they do not have energy to move, and changes occur more slowly.

So, with chromogenic photographs, what is incredibly important is to make sure that when these pieces are in storage, they are in the coldest temperature possible. That’s what hopefully will allow us to ensure that they don’t change while they are not on show. Because what is the point if, when no one can see them, we lose them?

Photograph showing a man and woman sitting on a rocky wall. A small slope with dirt and sparse trees rises behind them. The woman is wearing a red jumper; the man is in black. They are looking away from the camera.

Chromogenic prints were popular through the early 2000s, seen here in Hai Bo's series Lovers (2) (2001). © Hai Bo; M+ Sigg Collection, Hong Kong. By donation

Then, inkjet printing, which has been incredibly popular since the introduction of digital photography, bring us totally different reaction patterns. Most inkjet prints are fine in room temperature; you can have them at twenty degrees. They are of course sensitive to light, but in this case the main agent that will accelerate change is pollutants. The most interesting part is that pollutants are cumulative and reactive.

Photograph showing dense dark grey, cyan, and magenta dots on a white background in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Inkjet print’.

In inkjet printing, dyes or pigments are deposited on paper, rather than relying on exposure to light for chemical reaction

Let’s say a photograph is given to us by an artist in a paper or plastic tube of unknown composition, and we store it like that because it looks okay. Over the years, the tube would quietly disperse different toxic components, which would be absorbed into the print. When we eventually take the print out, frame it, and put it in an exhibition, we might see that the part of the print that was closest to the tube suddenly starts to change colour. Why? If the varnish of the frame was new, or if the paint of the wall was not dry for long enough, those pollutants could react with other ones already hosted by the photograph.

That is the issue of accumulative and reactive pollutants. One pollutant by itself might be okay, and nothing will happen for years. But as soon as this pollutant gets in contact with another pollutant, a chain of reactions can start. And at that point, there’s nothing we can do. We have to take action from the very beginning.

Photograph of two people fighting, surrounded by three broken-down and abandoned residential buildings.

Stanley Wong's Lanwei 19 / The Beasts / Taipei (2008) belongs to a series of archival inkjet prints. © anothermountainman (Stanley Wong Ping Pui); M+, Hong Kong. Gift of anothermountainman (Stanley Wong), 2012

A really high percentage of photographic conservation is prevention. You have to identify your photograph, because that will tell you what is going to put your photograph down. Then you can solve this prior to it happening. So, if I know that I have a chromogenic photograph, I will argue that you need cold storage. If I have an inkjet print, I will make sure that I have frames that have been off-gassing for a month, and the walls of the museum have to be dry. That is why as a photo conservator, you need to know how to look into the deepest layers of photographs. Identification, it’s vital.

Photograph showing a woman in a facemask leaning over a photograph. She is pointing a blue light at it with a small machine in one hand; in the other she is marking something down on paper.

Conservation technician Sally Hui filling in a condition report. Photo: Marta García Celma

What are some of the prevention problems specific to Hong Kong that you are facing?

Given the high humidity and temperature, I think that in Hong Kong—and this might be applicable not just for museum collections but for everyone—there are three major risks beyond colour changes: blocking, pest infestation, and mould.

Blocking is when the photograph is stuck to the glass. The top layer of a photograph is often gelatin, and gelatin is a hydrophilic material—when there is water in the environment, it just sucks it up. That higher concentration of water makes the top layer of the photograph become stickier, and if it dries in direct contact with the glass—which has small pores, glass is not sealed—it can become stuck.

If that happens, there is little we can do. So it’s always better to have the glass separated from the print by a spacer. You never ever want your glass in direct contact with a print. And even more so in a place like this one, where the humidity is so high for so many months of the year.

A really high percentage of photographic conservation is prevention.

Marta García Celma

The other thing that I’ve been seeing in quite a lot of items in Hong Kong—though not especially in our collection—is pests.

I’ve found photographs that have white holes, and I think, ‘Oh did someone scratch it?’ But when you look under the microscope or with a magnifier, you can see that there are little bites around it. Because pests are animals, and gelatin is an organic compound—it’s really yummy. If you were a pest and had to choose what to eat between plastic, cotton, and gelatin—which is like jello, it comes from animal collagen—you’d go for it!

For conservators, pests are not scary; they are actually giving us a lot of information about the environment. For example, if you start seeing silverfish every week, you know that is too humid and too hot. Maybe the air conditioner has gone off! So even when we don’t want them, pests are also helping us to manage the spaces where we keep our photographs.

Photograph showing a long, six-legged black bug with antennas on a white surface.

A pest seen around Hong Kong. Photo: Rebecca Yiu

Another super important damaging agent in Hong Kong is mould. If you have high humidity, high temperature, and poor ventilation, mould just grows. And mould is biological degradation; it’s a fungus. The fungi will start decomposing the gelatin of the photograph until the image is lost. Then it will go through the support.

If a conservator catches mould growth at an earlier stage, we can desiccate it; we cannot repair the damage, but we can ‘kill’ the mould spores and prevent it from expanding. But if someone has mould growth in a box with all the photographs in their house, and they don’t notice it, it will just expand through all of them, and that will be it. I mean it’s . . . gone.

It’s really important to be aware of these agents of deterioration when trying to protect our photographs—whether they’re artworks or family photographs. They are all so valuable.

Photograph showing a close-up of a dark surface. Across the top is white mould branching off in different directions like limbs of a tree.

Microscopic close-up of mould on a slide

What happens when the issue is no longer prevention? How do you treat surface damage?

If you have a tear, you will have to start by surface cleaning—dry surface cleaning, and a wet cleaning—and then opening up the fibres, pulling the fibres together, and then sealing it in the back. You won’t be able to just fix the tear, because first you have to clean the area. It’s really like in medicine: you cannot stitch a leg if you haven’t disinfected it first.

Photograph showing a woman in a facemask and gloves brushing a circular photograph with a large dry paintbrush. She holds a small light in her other hand.

García Celma cleaning a photograph. Photo: Manami Hori

A common issue we see in photography conservation is when the edges of the photograph have started delaminating and flaking. This is when the top gelatin and baryta layers start cracking and start to come off like the shell of an egg. Then you can see the fibres of the paper behind it. While these are signs of handling and are part of the history of the photograph, the fact that these fibres are open means it’s a direct access point for air, pollutants, and moisture to enter the work.

In these cases, we consolidate it with gelatin. We carefully deposit warm, liquid gelatin over the cracks and wait until it dries and seals. For all treatments, we always try to use a material that is firstly sympathetic to the original one, so that when changes occur due to environmental factors, they will be as equal as possible. Secondly, we want the treatment to be reversible, so that if in the future it needs to be undone, there is no permanent change.

Photo Conservation: Gelatin Consolidation
Photo Conservation: Gelatin Consolidation
4:54

García Celma consolidating the worn corner of a photograph with gelatin. Conservators typically handle artworks with gloves, but in cases like this, the fibres from the glove fabric could contaminate the process; she is working with sterilised hands instead

There are cases in which photographs might need an infill in an area that has been deeply scratched or skinned. Sometimes, these are caused backpacks worn by visitors to the museum. That’s why many museums say, ‘Please do not wear your backpack. Put it in the locker.’ It’s not because we’re afraid you will steal something in your bag; it’s because you might damage something, and not all works are framed or have glazing.

Sometimes, curators choose to show a photograph even when it has a scratch, and I think that’s great. Aesthetically, it may not be perfect, but the material is not in a bad state. It’s like if you have a healthy person that had a really bad burn. The scratch is still part of the object’s story.

Photograph showing a deep scratch on film in close-up.

A deep scratch on a chromogenic print

Photograph showing micro-scratches in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Micro scratches on a silver gelatine print’.

Micro-scratches on a gelatin silver print

Photograph showing layers of paper exposed by a fold in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Detail of a fold on a resin coated (RC) paper. Silver gelatine print.’

Folds can leave deep scars on prints, such as this is a fold on resin-coated paper

Photograph showing a dark surface with a fold filled in with a black substance in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Previous retouching / inpainting’.

Sometimes, artists attempt to fill folds and scratches in on their own before they arrive at the museum. ‘Some of them might have painted with a really good pigment,’ says García Celma. ‘Some of them just took the black pen they had next to them—or a green one!’

Photograph showing a deep scratch on film in close-up.

A deep scratch on a chromogenic print

Photograph showing micro-scratches in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Micro scratches on a silver gelatine print’.

Micro-scratches on a gelatin silver print

Photograph showing layers of paper exposed by a fold in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Detail of a fold on a resin coated (RC) paper. Silver gelatine print.’

Folds can leave deep scars on prints, such as this is a fold on resin-coated paper

Photograph showing a dark surface with a fold filled in with a black substance in close-up. There is a magnification scale in the bottom left corner labelled ‘0.2mm’. Along the bottom is the label ‘Previous retouching / inpainting’.

Sometimes, artists attempt to fill folds and scratches in on their own before they arrive at the museum. ‘Some of them might have painted with a really good pigment,’ says García Celma. ‘Some of them just took the black pen they had next to them—or a green one!’

Conservation decisions are always made by consulting with the curators and even the artists. Some changes may be relevant for the storytelling of an artwork; others may accidentally pull the artwork away from its original intent. One person cannot decide everything: collaboration makes for the best conservation.

Can you tell me about some of the favourite things you’ve worked on so far at M+?

This photograph, I love it: it’s by Cecil Beaton. The depth and intensity of his gaze—it’s like he’s looking at you. And this one, by Yau Leung.

Two photographs side-by-side. The one on the left shows a man with a large nose and long white beard looking intently into the camera. The one on the right shows a figure walking through an empty intersection.

(Left) British photographer Cecil Beaton’s The Years Between—A Beaton in Fukien province (1944) and (right) Hong Kong photographer Yau Leung’s Wrong Way (unknown date). Both are gelatin silver prints. © Cecil Beaton Studio Archive at Sotheby's / © Photo Pictorial Publishers Ltd.

These are not the most contemporary artworks we currently care for; they are small gelatin silver prints. But these works are magnificent. They speak a lot. They pull you back to that moment, that space.

But a second layer—things that the public cannot see—is that most of these photographs will have tears and folds. Most of these photographs seem quite damaged in the front: they might have scratches, and tape marks, and the edges might be flaking.

There is a reason why these photographs have all this damage. If you look at the back, they have many different stamps. This reflects the time in which photographers were trying to put their photographs within the art market, or in competitions.

They would simply take the photograph, put it in an envelope, and ship it. It would get folded. It would get smashed. And if their photograph was selected, then it would get put on the wall many times with a pin or tape. And on the back of the photograph, there would be a note or the stamp of the gallery where they sent it, and a date. Or if they were part of a journalistic project, they may show hand-painted cropping marks and information about the scene.

Two photographs side-by-side, each showing the back side of a photograph. Each is marked with various stamps and labels.

Photographs are often received with descriptions or stamps on the back. Cecil Beaton’s The Years Between (left) is stamped by Gallery Naruyama and Camera Press; Yau Leung’s Wrong Way is stamped ‘15th Singapore Salon 1964’. © Cecil Beaton Studio Archive at Sotheby's / © Photo Pictorial Publishers Ltd.

None of these photographs are pristine. Not even the ones by Fan Ho. But when they come out of storage, they make you be silent. They have a power. And when treating them, these are the days when I realise how lucky I am, the fact that I am so close and can take care of these artworks.

When they are framed and hung on the walls of the museum, they become statements. But when they are at the conservation lab, I’m seeing them unframed—this fragile piece of paper with a tear in the corner. Conservators are lucky enough that we can see the vulnerability of these items.

Photograph showing an unframed photograph on a white-lined table. Around the photograph are various tools, such as a head magnifier, bottles and beakers, erasers, sponge, and gloves.

Some of the tools used in photo treatment: erasers for dry cleaning (left centre); a UV torch (left) for identifying areas with cracked gelatin needing consolidation; ethanol and water (top left) used for localised humidification and wet cleaning; and a head magnifier (top right). Photo: Marta García Celma

What makes conserving an artwork for a museum different from conserving one for home?

What I think is different between vernacular photography—like people’s photographs or day-to-day photography—and contemporary art photography is the need for display. For example, if treating a private person’s photographs of their ancestors, it can be assumed that the owner will want to have these works constantly in their living room, or in an album to look at them often. I know that, for individuals, having photographs in storage is not the point, because they will not want to conserve a photo if they are not going to look at it. In these cases, conservators would advise how to frame them and where they can put it: never have it directly facing a window, never have it on top of a radiator, and so on.

In the museum, we are still doing that, but at a different scale. We advise how long a photograph can be on show to make sure that it retains its current look for whatever the preservation target of the museum is. If it’s a 200-year or 500-year or 1,000-year preservation target, that’s the number of years that we want our artworks to be in the same visual condition.

What can people outside the museum do to care for their photographs?

If there is something that I could say—it would be for collectors, for artists, and for people in general—is try to gather as much information about the long preservation of your photographs. Don’t be afraid to search and to ask questions—there is plenty of information online about basic ways of preserving your photographs. They always follow the same four environmental factors: temperature, humidity, pollutants, and light. There are even websites that can help you identify what kind of pests you have, and what they’re attracted to.

If you’re an artist, make sure when you produce an artwork, you record what you are producing and how, and follow the standards for each photographic process. If it’s a print that needs to be washed, wash it for long enough so that all the chemical residues are removed and will not react in the future. If you use digital printing techniques, follow the advice of the manufacturers in regards to paper and inks combination.

No one told us that these 'things' were going to decay so fast.

Marta García Celma

If it’s a personal photograph that you care about, don’t leave it in a humid space; leave it in a place that has constant airflow, away from direct sunlight, in a frame with a spacer between the glazing and the print.

At M+, I mostly care about contemporary artworks, but I think that all types of photographs are incredibly valuable for many different reasons. Many people don’t know what photographs they have, and how to care for them. No one told us that these ‘things’ were going to decay so fast.

So what I’d like to say to everyone is: Please, please, please take care of your photographs (before they start changing)!

As told to Gloria Furness (Editor, Web Content). The above interview has been edited for clarity. All microscopic photos: Marta García Celma.

Marta García Celma is the Conservator, Photography at M+.

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