Caring for paintings and frames

All museums have paintings. Paintings can be on wood, canvas, ivory, ceramic, or vellum. This guide examines how to look after easel paintings, defined here as any painting that can be moved, and their frames.

If paintings appear in your collection, your workforce should understand how to care for them and their frames, how they are constructed, what issues might arise, and how to handle them.

You can often identify common problems with the human eye. Monitor your art collection with a magnifying glass, a torch held at a raking angle to show surface deformations, and a pencil, paper, and camera to record any changes or damage. Keep an ordered list of your paintings and their potential problems so you can bring specific issues to painting and frame conservators.

Catching damage or deformity early makes a significant difference to the long-term wellbeing of paintings and frames. It also helps retain original material that might otherwise detach and be lost.

Paintings and frames face two main categories of threat: environmental and biological. Environmental threats come from the conditions around the object, including light, relative humidity, temperature, and air quality. Biological threats come from living organisms, mainly woodworm and mould. With care and attention, you can put simple precautions in place to protect against both.

Environmental threats

Paint is vulnerable to a wide range of environmental threats and shows damage from high relative humidity, light, and biological activity. With care and attention, you can put simple precautions in place to protect paintings and frames.

How does light damage paintings and frames?

Lighting museums and galleries correctly is an essential part of collections care. Materials used in paintings vary in their sensitivity to visible light, infrared, and UV. Some pigments are stable, or lightfast, while others fade even at low light levels. UV is the most damaging.

Light damage is both cumulative and irreversible. It takes only decades for the most sensitive colours to fade. Keep light levels as low as tolerable to slow the rate of fading. High levels lead to rapid colour loss. Frames generally remain stable in light levels that would damage paintings, unless finished with organic materials such as wood or animal veneers. The MGS guide to conservation and lighting explains how to set appropriate light levels.

Lighting guidelines:

• Keep light levels for paintings at or below the recommended intensity of 200 lux
• Reduce the time a painting is exposed when this is not achievable, to counter cumulative damage
• Apply UV-absorbing film to windows to reduce the damage done by ultraviolet in daylight. Aim to exclude UV completely.
• Control daylight with window blinds
• Fit low-UV emitting tubes when using artificial lighting
• Use track lighting, which produces cooler and more diffuse light than spotlights
• Do not expose paintings to unfiltered UV-emitting fluorescent lamps
• Do not use individual picture lights, as they produce hot spots on the surfaces of paintings and frames
• Take measures to reduce the heat emitted if using incandescent lights

How does relative humidity damage paintings and frames?

Relative humidity (RH) measures how wet or dry the air is. Monitoring and controlling RH is essential to preserving both paintings and frames.

When RH fluctuates, it causes many materials in the painting to expand and contract. Wood, gesso, and fabric readily absorb moisture from the air, which causes this growing and shrinking and ultimately weakens the materials.

Paint can crack or flake as a result of the supporting materials expanding and contracting. Canvas can become slack and sag, frame joints and wooden panels can open or split, and gilding can deteriorate quickly.

Follow these guidelines to prevent this often-irreparable damage:

• Aim for RH between 50 and 60% for both stores and display areas
• Use humidification or dehumidification equipment if necessary
• Keep paintings well ventilated and do not stack them close together in storage, as mould typically grows at an RH of 65% or above
• Watch for corrosion of metal supports, nails, and hanging chains, which high RH encourages
• Watch for a white bloom on the varnish surface, which damp can encourage
• Be aware that low RH causes paintings to dry out and become brittle, making them susceptible to damage
• Be aware that low RH can also damage frames by causing the joints to dry out and open up

How does temperature damage paintings and frames?

Temperature affects paintings and frames by changing the RH and damaging some materials.

Follow these guidelines for controlling temperature:

• Keep to a human comfort temperature of around 20°C, as sudden fluctuations can be damaging
• Keep any temperature fluctuations to a minimum. Adjust conditions using low-level conservation heating.
• Use blinds to reduce heat gain and loss
• Do not hang paintings above heat sources, as the rising hot air carries dirt
• Be aware that sub-zero temperatures can cause acrylic paintings to grow brittle and crack
• Be aware that high ambient temperatures can soften paint and other materials, which then causes dirt to stick and become absorbed into the work
• Be aware that excessive heat dries paintings and speeds up natural ageing

How does air quality damage paintings and frames?

Pollutants in the form of gases and particles can cause or accelerate deterioration in paintings, as chemicals react and cause discolouration and fading.

Gaseous pollutants are not a high risk for paintings and frames, but be aware that impure gold leaf is more likely to tarnish than pure gilding. High visitor numbers and poor housekeeping can lead to a build-up of dust, which is more dangerous to paintings and frames. The mixture of particles attracts moisture and can become absorbed into the artwork.

Remember these points when protecting your paintings from pollution:

• Good housekeeping is the best prevention against dust pollutants
• Door seals and dust-trap mats stop a large amount of external pollutants
• Fit glass in frames to protect particularly vulnerable, unvarnished paintings
• Hold a piece of card against the gilded edges when cleaning glass in frames, to protect from abrasion
• Never clean the surface of a painting, even to remove dust, as it can remove paint and varnish. Seek expert advice.
• Do not dust frames, particularly with cloths, as dust contains abrasive particles that will abrade fragile gilded surfaces
• Be aware that oil gilding is damaged by organic solvents such as turpentine and white spirit
• Be aware that water gilding is easily damaged by moisture
• Be aware that unvarnished paint surfaces, especially acrylic paint, attract and absorb dust, becoming engrained, sometimes irreversibly

Biological threats

How do pests damage paintings and frames?

Woodworm

Wood is everywhere in paintings: in the stretchers, strainers, frames, and panel supports. All wood is susceptible to woodworm, which you will notice by the presence of frass, a fine sawdust-like debris, and small holes where the adults have exited the wood.

When tackling woodworm, remember:

• Adult beetles are usually active in late spring and early summer. Check more often around these times and align housekeeping and checks to them.
• Females compromise the structure of wood by laying eggs in it. These turn into burrowing larvae that feed on the wood.
• Adults make the holes in wood when they emerge after two years developing inside it. Woodworm can be dormant in unfavourable conditions, so even older-looking holes could see activity at a later date.

How does mould damage paintings and frames?

Mould readily develops on paintings and frames where the relative humidity is above 65% and conditions such as poor airflow and a food source are present. You will find it on the backs of canvases, attracted to dust and the size coating. Pay particular attention to glazed paintings, as micro-climates can form between the paint and glass, or inside the glass itself.

Minimising biological threats:

• Isolate a painting or frame with active woodworm, wrap it with museum-standard materials, and move it to a quarantine area for further assessment by conservators
• Follow the same procedures for items affected by mould, except keep them in a well-ventilated space and away from other material
• Dry mould-affected items out slowly to deactivate the mould
• Keep RH levels below 65% to prevent the outbreak of mould
• Always contact a conservator to treat paintings or frames that show signs of mould or woodworm
• Be aware that insects can leave very acidic material, including excrement called fly specks
• Wear mouth and nose protection when dealing with mould, to avoid ingesting spores

One of the biggest threats to the conservation of paintings and frames comes from people. Take simple precautions to eliminate accidental or purposeful damage to your collections.

How to store paintings and frames:

• Hang paintings on an internal wall, rack, or hanging system on S hooks to allow space and ventilation behind the painting. Keep away from draughts. This is the best way to store a painting.
• Always store paintings and frames vertically, unless a paint layer is unstable, in which case store horizontally, off the ground, preferably on blocks to allow airflow, and contact a conservator
• Attach S hooks, not stretchers or strainers, to framed paintings on sliding rack systems, to allow for some movement from vibrations or the environment
• Do not overfill pigeon-hole-style storage. Use Plastazote or foam blocks to allow some give for ornate frames.
• Store paintings according to size and do not over-stack
• Put a rigid interleaf of chemically stable materials between paintings to prevent pressure damage to gilding or decorative details
• Do not store framed and unframed paintings in the same section
• Remove protruding hooks, nails, and chains if necessary
• Use high-density foam blocks to raise paintings at least 20cm off the floor if they must be stored against a wall, to reduce damage from floor cleaning
• Stack in descending order of size
• Stack paintings front-to-front and back-to-back, with interleaves in between
• Use appropriate wrapping to cushion the corners of vulnerable frames
• Avoid stacking under windows, near doors and radiators, or in regularly used walkways
• Make sure accession numbers and details are easily visible to prevent unwarranted handling
• Keep stores free from birds and rodents and run a robust integrated pest management (IPM) programme. The MGS guide to pest management explains how to set one up.

How to handle paintings and frames

Museums handle objects often. They are moved for installation, put into storage, and rearranged for exhibitions or redecoration. Anyone handling paintings and frames should be trained in the appropriate procedures.

Simple common sense goes a long way. Plan ahead, take your time, and clear your walking routes and destination of obstacles. Make sure there are enough people to allow staff to stop for a rest while moving an item. Always stand a painting or frame on blocks, not the floor.

Decide in advance whether the painting is secure enough to be moved. Check that it is secure in its fitting and that no stretcher keys are loose.

Handling considerations:

• One person can handle small paintings, but only carry one painting at a time. Working in pairs lets the other person open doors.
• Wear close-fitting nitrile gloves to prevent transfer of oils from skin, and change them if they get dirty
• Hold one bottom edge and one vertical edge. Never carry a painting by the top of a frame.
• Never touch the surface of a painting or the back of its canvas or panel
• Carrying larger paintings requires more than one person and a clear leader
• Use the blocks on the back of a frame when handling the painting
• Use webbing straps or trolleys if appropriate
• Carry flaking paintings horizontally and move them to a flat storage space. Contact a conservator to secure the paint.
• Secure the section with acid-free tissue before moving a painting with loose mould
• Never let tape come into contact with gilded or decorative surfaces or the painted side of the painting. Use cotton tape where possible.
• Gather the pieces if damage occurs, no matter how small, and identify where they came from. Bag, label, and tie them onto the back of the frame with cotton tape.

How to pack paintings and frames

The underlying principle of wrapping paintings is to protect vulnerable surfaces from puncturing. Packing also protects paintings from changes in heat, cold, and moisture.

The destination, distance, and transport all determine the level of packing and materials required. Packing crates offer a high level of security and physical protection, but they are heavy to move, which risks them being dropped, and they can be expensive.

Protect paintings and frames against changes in relative humidity and temperature when they go into storage. Packing helps do this.

Always keep stocks of museum-standard soft packing materials, such as:

• Bubblewrap®
• Jiffyfoam®
• Acid-free tissue
• Polyester film (12 micron Melinex®)
• Polythene
• Low-tack tape
• Parcel tape
• Cotton tape
• Glass and fragile tape

Packing guidelines:

• Use an interleaf such as acid-free tissue or Melinex® around the gilding of frames and over the paint surface of unframed paintings. Applying cotton tape first prevents it touching unglazed paintings.
• Use Bubblewrap® or Jiffyfoam® to make protective corners
• Make temporary backboards if a painting does not have one, and cover the painting and frame with a protective environmental layer such as plastic sheeting
• Protect glass with low-tack tape and label it with glass tape on the packaging as a warning to handlers
• Label frames and packaging appropriately to prevent confusion, especially if you obscure the image
• Label packages on the back and front
• Always retain existing labels, even fragments, for the information they contain. Put them in archival sleeves, number them, and keep them with the painting or frame.
• Do not use Bubblewrap® directly against paint surfaces, though you can use it over a tissue layer
• Do not let any adhesives or tape touch gilded surfaces or painted canvas
• Never stick labels directly onto the back of canvases or panels
• Do not try to remove labels from the back of canvases or panels

How to transport paintings and frames

Museums can take basic steps to ensure good practice when employing couriers and transporters:

• Ask conservators and curators for recommended couriers who have experience transporting artworks and who hold the necessary insurance and qualifications
• Ask couriers for their risk assessments and method statements (RAMS) and make sure you are happy they understand your needs. Explain your transportation requirements to them.
• Look for couriers with clean, well-equipped vehicles that have plenty of padding and no loose items or items from other jobs
• Build a relationship with couriers so they understand your museum’s specific requirements
• Secure paintings to the side of vans with flat webbing and additional padding, and raise them from the ground to absorb vehicle vibrations
• Do not allow paintings to travel if they are inadequately packed
• Make sure vans are heated in cold weather, as sub-zero temperatures can damage acrylic paints

Correct framing can contribute significantly to the preservation of a painting.

Any painting that is poorly fitted, not secure in its frame, or unprotected at the back is vulnerable to damage. Even simple procedures such as attaching metal brackets carry risks. If the screws are too long or the holes too deep, frames can be damaged.

Art technicians or conservators should carry out re-fittings, as they understand the unique needs of different materials and techniques and will fit robust fixings that take the weight of the painting. The Conservation Register lists accredited conservators.

Refitting specifications:

• Pad rebates to prevent friction on the face of the painting
• Pack spaces around the sides of the painting with suitable material to avoid movement within the frame
• Use only metal brackets or plates to secure paintings within frames. Hammers, nails, and staplers can cause dangerous vibrations.
• Never secure plates directly to the painting. Hold paintings in by pressure alone, allowing for expansion or contraction of the support. Think more carefully about plates on multi-panel artwork.
• Fit backboards in suitable materials such as Correx®, Fome-cor®, or hardboard to protect the reverse of a painting. This also keeps out dirt and buffers against vibration, shock, and RH fluctuations.

Considerations for fitting glass:

Only a qualified framer, art technician, or conservator should fit glazing. Not all frames can accommodate glass, which is heavy and requires fixings to keep it in place. Consider the following:

• Is the frame sound and strong enough to support the weight of glass?
• If not, can the frame be adapted to take the extra weight without damaging or devaluing it?
• Consider an acrylic cover if glass is too heavy
• Leave space between the glass and the surface of the painting, using check sticks or spacers
• Decide on a thickness of glass suitable for the frame
• Consider laminated or toughened glass for extra protection
• Consider UV-filtered and low-reflecting glass to protect against light damage
• Think about how glazing might affect your lighting system, as glazing can be very reflective
• Do not use spray cleaners on glazing, as this will damage the gold layers on gilded frames

Ask a conservator

If you have any doubts about preserving and protecting a frame, consult an expert. Accredited conservators have years of experience in their particular fields and can offer valuable advice. You can find one through the Conservation Register.

Resist the temptation to carry out basic procedures yourself, as even simple treatment can cause unforeseen damage. Something as simple as tightening a slack canvas can result in tearing, over-expansion, or split tacking margins.

Depending on your workforce and planned programme of work, it can make financial sense to train staff or volunteers in collections care practices such as housekeeping, handling, documentation, and basic condition checking. Discuss your training needs with a conservator.

Methods for supporting paintings have changed over the centuries. This section outlines the most common materials and components of painting supports and explains how they might deteriorate over time. A glossary at the end of this guide defines some of the terms used.

Auxiliary or secondary supports

These terms describe the wooden structures a canvas is attached to. The canvas or fabric is usually attached to a wooden stretcher or strainer using tacks or staples. This component is usually invisible but carries significant risks of deterioration.

Look out for:

• Woodworm infestation, signified by frass and flight exit holes
• Splits in the wood caused by inappropriate display or handling
• Warping caused by fluctuating relative humidity
• Rusting or missing tacks
• Dropped or missing stretcher keys

Fabric supports

Canvases have changed over the last two centuries. Originally they were made of flax and 100% linen. The quality of painting fabrics became much more inconsistent from the mid-19th century onwards, as mechanised production methods and inferior fibres made canvases less durable. Since then, canvas lining has been introduced to help conserve poor-quality fabrics and support repairs and deformations.

Fabric supports deteriorate in unfavourable conditions. Fluctuating relative humidity and temperature can cause planar deformations, delamination between original and lining canvases, and mould.

Incorrectly mounted canvases can develop holes or splits in the tacking margins. Canvas distortions can also occur if stretcher keys drop between the canvas and supports.

Although many painting fabrics are durable, poor handling can lead to punctures, tears, and cracking of paint from accidental knocking, impact, or items going through the canvas.

Rigid primary supports

In the 19th century, colourmen introduced millboard panels and other mass-produced rigid supports. As new materials developed, the 20th century saw the use of hardboard, plywood, and other reconstituted materials. Other rigid supports include glass, metal, and ivory.

If your painting is on a rigid primary support, be aware of deterioration risks such as:

• Movement along wooden panel joins
• Splits within panels
• Woodworm and other pest damage
• Distortions caused by cradles

Weak or delaminating corners on manufactured boards

All paintings are made from hygroscopic materials, and all of them deteriorate in some way. Each layer of a painting poses some risk of deterioration. This section outlines the main materials in paintings and their associated issues.

Preparatory layers

Size

Size is an invisible solution used for stiffening fabrics and canvases. It reduces the absorption of priming, paint, and varnish into the fabric. Size can deteriorate as a result of direct water damage or high relative humidity, and can occasionally cause priming and paint to delaminate from the canvas.

Priming and ground layers

These serve two functions: they provide a suitable surface to apply paint, and they create a tonal base for the composition. This is generally a stable layer, but if the artist used experimental materials, the paint could flake or tent.

Paint layers

Paint is a mixture of pigment and medium. The medium varies according to the type of paint. Oil paint binds using linseed oil, watercolour uses gum arabic, and acrylic uses a synthetic resin.

The stability of a paint layer depends on its method of application, any adulteration with additives, and its environment. Many conservators specialise in the deterioration of paint and can identify problems based on the shape and type of cracking. Consult one of these experts if you are unsure of the issues facing your paintings.

The glossary at the end of this guide explains the following terms used to describe deterioration in paint:

• Flaking
• Stretcher marks
• Cupping
• Tenting
• Blistering
• Cleavage
• Drying cracks
• Alligator cracks
• Craquelure

Varnish layers

Most paintings are finished with some kind of varnish to give extra depth and offer additional protection. Historically, varnishes were made using natural resins such as dammar and dusk, but synthetic resin varnishes became commonplace in the 20th century.

Varnishes are usually clear on application but can discolour with age. Natural resin varnish yellows significantly, altering the tonal values of paintings and distorting the appearance of colours. From the late 19th century onwards, some artists preferred to leave paint surfaces unvarnished. Look out for blooming, blanching, and degradation, especially where light intensity, particularly UV, is high.

An original frame is an integral and historical part of an artwork. It isolates the painting visually, separating it from its surroundings with a decorative design that enhances and protects the work.

The diversity of framing materials means museums and galleries can hold a wide array of frame types and finishes. This section outlines some of the materials you might find on frames.

Substrate or base materials

Composition, wood, and papier-mâché are the predominant materials for creating a substrate, or base, for a frame. Most problems with frames emerge from deterioration of the substrate.

Be aware of the following risks with base materials:

• Open mitre joints
• Splits in the frame, caused by either bad handling or fluctuating relative humidity
• Woodworm or other insect damage and infestations, indicated by frass
• Holes and missing areas from old fixings
• Rusted or damaged screws, and poor repairs

Gesso

Gesso is a mixture of whiting and size applied to the substrate to create a smooth surface for applying gold leaf when gilding a frame. Several coats of gesso are often applied, each slightly thinner than the last. Once dry, gesso takes on a plaster-like appearance. It is then smoothed until the frame has a surface smooth enough for gilding.

When exposed to fluctuating relative humidity, the substrate frame can distort and gesso can begin to flake from the frame, taking gilding with it.

Bole

Bole is a mixture of fine clay and size applied on top of gesso. It contributes to the final appearance of the gilding or can be polished as a decorative finish. Yellow bole is usually associated with oil gilding, and yellow, red, and black bole with water gilding, though other colours were also used. Bole itself is stable, but it can flake or raise if applied to unstable gesso or if the substrate is damaged.

Gilding

Gilding is the process of applying gold leaf to give frames the appearance of being made of gold. Water gilding and oil gilding are the two techniques, and they result in slightly different appearances. Both require gold size to act as an adhesive for the gold leaf.

The differences between the two are subtle. Water gilding is burnished and placed over coloured boles, while oil gilding is often left matt and used on composition frames or less raised areas of the frame.

Gilding can flake if the relative humidity is unstable, but it is more likely to be damaged by bad handling, cleaning, or dusting, where it can receive scratches and abrasion.

Toning layers

This delicate final layer is a slightly pigmented glaze applied over gold leaf. Toning layers are easily damaged when cleaning. Look out for patchy surfaces, fine curling, and flaking leaf as a result of poor handling and over-cleaning.

Do not confuse toning layers with coatings. Coatings were added many years later in an attempt to revive old frames, usually a paint or powder suspended in varnish that darkens as it ages. Avoid coatings, as they can damage the gilding and are hard to remove.

Paintings and frames are especially vulnerable in a fire or flood. A robust, active emergency plan that identifies hazards and sets out how to reduce or respond to them is essential.

The Scottish Council on Archives has produced emergency planning guidance for collections with practical advice on preparing for incidents.

Scotland has dedicated networks for specialist help during emergencies. Find contact details on the Scottish Council on Archives page listing emergency response networks across Scotland.

For more collections care guidance, find our other advice guides on collections.

The Collections Trust provides a wide range of guidance and advice on collections care.

The Institute of Conservation has produced collections care guidance for frames and gilding, covering the materials and finishes found on historic frames.

The National Gallery has produced guidance on caring for paintings and their environment, with detailed advice on display and environmental conditions.