Introduction to Art Restoration & Conservation

Our conservation laboratory employs 15 full-time conservators

In this picture, a “dry” area where treatments not requiring water or chemicals are conducted.

Our state-of-the-art conservation laboratory and art preparation area employs 15 full-time conservators, apprentices and preparators who treat paintings on canvas, works of art, documents and objects on paper, as well as all kinds of photographic mediums. 

Many of us possess a treasured heirloom or work of art that has suffered damage. Perhaps it is an old and valuable letter or document, creased and torn from repeated folding and unfolding, yellowed and embrittled by an acid content. Or maybe it is an antique print such as a Currier and Ives, improperly framed 75 years ago. Now, it is stained with brown speckling, called foxing, and dark brown vertical lines transferred from the old wooden shingles used to back the frame. Or it could be a photograph that was stored in a basement and damaged by water, a wavy brown tide mark discoloring the paper or canvas. Often, pieces such as these are considered a loss because their owners are not aware that the damage can be stabilized, and in many cases effectively reversed.

Acid staining on a Edward Curtis photogravure

A photogravure by Edward Curtis with a mat burn

This photogravure exhibits a classic mat burn. It was previously matted in an acidic mat made of wood pulp fibers and prolonged contact with the mat caused the acid to migrate into the artwork sheet. Although the high-quality paper was inherently acid-free, it had assumed the characteristics of an acidic paper. After treatment, staining has been reversed and the paper deacidified by aqueous treatments. 

Joel Oppenheimer, Inc. is a nationally renowned art facility

About Our Restoration Services

Joel Oppenheimer, Inc., a nationally renowned art facility, was founded in 1969 by the conservator for the Department of Prints and Drawings of the Art Institute of Chicago to fulfill a need for professional conservation services in the private sector. We maintain an apprenticeship program and train our own staff, all of whom hold degrees in fine art and art history. Our staff can analyze and perform corrective treatments for anything on paper or canvas. This includes drawings, prints, maps, photographs, documents, paintings and Asian screens. Our laboratories have developed and perfected techniques for restoration of paper, canvas and photographs that enable us to retain delicate pigments, signatures and hand coloring.

With our expertise in both art and science, Joel Oppenheimer, Inc. employs the attention to detail of old-world craftsmanship while utilizing state-of-the-art technology. Each piece and problem is treated with singular care. Our clients include major museums that require our particular expertise, smaller museums that do not have their own conservation facilities, galleries, institutions and private collectors nationwide.

On this webpage, we take you on a tour inside our laboratories showing you examples before, during and after treatments were performed. We also answer many frequently asked questions; help you to identify the kinds of damage that can occur to paintings, photographs and works on paper; and explain what can be done to prevent and remedy these problems. With a broader knowledge of the principles of conservation and restoration, collectors can better preserve and care for their valued works of art and family heirlooms.

Conservation and Restoration

Art conservation and restoration involve the preservation of works of art, arresting progressive deterioration that causes damage and correcting damage that has previously occurred. 

Before treatment
After treatment

Treatment of a Lithograph by Toulouse-Lautrec

Before Treatment: (Left) This lithograph had multiple problems. It was darkened due to an acid content in the paper, cockled, and stained from water damage. Improper backing with linen had, over time, caused the paper to tear and fragment.

After Treatment: (Right) The linen and glues were removed employing aqueous treatments, an example of conservation. Staining and cockling were reversed by chemical and aqueous methods, which are restoration techniques. Finally, the sheet was supported with a thin layer of mulberry tissue applied with a neutral-pH, starch-based adhesive to complete the treatment.

Art conservation and restoration involves the preservation of works of art, arresting progressive deterioration that causes damage, and correcting damage that has previously occurred. Fine art restoration is divided into specific areas of expertise. Restoring a painting, photograph or drawing, for instance, is in essence solving a problem related to the substrate, or material on which the piece is executed, as well as the medium or emulsion layer that is applied to that substrate.

What Is the Difference Between Conservation and Restoration?

In art conservation, the objective is to arrest any progressive deterioration that is occurring so that the piece in question will remain intact, as it is, for as long as possible given what we know today. An example of conservation would be mending a tear using mulberry tissue and a neutral-pH, starch-based adhesive to prevent the tear from enlarging due to the natural expansion and contraction that occurs from variations in temperature and humidity levels in a sheet of paper. Another example of conservation would be deacidification, a chemical stabilization process.

Restoration involves a cosmetic treatment that is intended to return the object to its original appearance, while retaining any patina of age that is considered an attribute. For instance, if a tear has progressed in a manner that detracts from the composition of the piece, we can graft new paper fibers into the tear, rendering it nearly invisible, thus restoring the object. An example of painting restoration would be replacing pigment losses to match the original as closely as possible. Restoration of a photograph may include a chemical bleaching and redevelopment process, as well as simulating a new emulsion surface.

Backing a Work of Art on Paper with Mulberry Tissue

Backing a work of art

Step 1

First, the work of art is saturated with water allowing the fibers to expand and become receptive to the adhesive. Wheat paste, a neutral-pH, starch-based adhesive, is then applied to the verso of a work of art preparing the sheet to be backed with mulberry tissue.

Backing artwork step 2

Step 2

Then, mulberry tissue is skillfully applied, avoiding the formation of undesirable folds or crimps.

Step 3

Finally, a stippling process utilizing specially designed boar hair brushes meshes the fibers of the original sheet, which are expanded by introducing moisture, with the fibers of the backing tissue. Thus, a bond is formed allowing the original sheet and backing material to expand and contract together as one sheet when exposed to temperature and humidity changes.

Corrective Treatments

What causes damage to works of art and how can they be properly conserved or restored?

Treatment of An Antique Oil Portrait

Before Treatment: (Picture 1) This painting exhibited multiple problems. Dulled by an old, discolored natural resin varnish, the linen substrate was embrittled and rotted from severe atmospheric damage. Consequently, the paint was cupping and crackled due to high humidity and extreme temperature differentials. (Picture 2) A detail of a severe curvilinear tear in the portrait area.

After Treatment: (Picture 3) The portrait detail shows the puncture mended with a
nylon-based fiber. A mold was taken from the healthy canvas and transferred to the
repaired area duplicating the original surface. Pigment losses were replaced and a final synthetic resin varnish layer applied. (Picture 4) In this detail after treatment, the linen has been relined and stabilized and old varnish layers have been removed.

The causes of damage to works on paper, paintings and photographs may often be the same, but the resulting problems can vary due to the relationship between the pigment layer and the substrate, and when present, the ground layer. Many of these conditions that threaten preservation or cause deterioration are not obvious.

To uncover a few of the hidden enemies of family heirlooms and works of art of all mediums one has only to look around their home. Each of us is familiar with one or more of these detrimental circumstances: pictures stored in a hot, dry attic, or in a basement with its inherent dampness; improperly framed pictures; family photographs mounted in acidic albums with damaging adhesives; heirloom letters and documents, folded, torn and stained from exposure to moisture, relegated to a dresser drawer. When properly made and cared for paper, canvas or linen can last for centuries. However, they are extremely vulnerable to damage caused by improper storage and environmental factors.

Environmental Factors
Humidity: Exposure to excessive humidity can allow mold to form. Mold forms when humidity levels are sustained above 70%. Appropriate air conditioning or dehumidification will help prevent the formation of mold. Foxing, a brownish speckling that is caused by the chemical action of mold on colorless iron salts present in most paper, is an obvious sign of mold. The mold not only discolors the paper, but also feeds on sizing and paper fibers, thereby weakening the molecular structure of the sheet. Also, mold can penetrate the pigment layer of a painting and feed on the sizing in the canvas from the verso.

Moisture: Since most materials expand with moisture, a severe waviness or rolling of paper, called cockling, may occur when it is exposed to excessive humidity or moisture. When cockling is severe or mold is observed, the piece should be given to a conservator for flattening and thymolization, an anti-fungus vapor treatment. Trapped moisture between varnish and pigment layers of a painting can result in blooming, a whitish-gray film, and greatly reduce the aesthetic quality of a piece.

Light: Ultraviolet light causes fading, yellowing and embrittlement. It also greatly accelerates the effects of an acidic content. Fluorescent and sun light are the most harmful. Care should be taken where a piece is placed so that direct natural light is avoided. Ask your framer about using ultraviolet filtering glass or Plexiglas to limit exposure to ultraviolet light. While opaque pigments in paintings are less susceptible to fading, transparent glazes and varnish layers may be affected by ultraviolet exposure.

Heat: High temperatures accelerate deterioration of paper and embrittlement of paint layers. Works of art should not be stored or exhibited near a heat source. Heat also accelerates the damaging effects of an acidic content.

Air Pollution: Pollutants in the atmosphere can cause discoloration, embrittlement and eventual disintegration of paper fibers. More commonly, however, solid matter (dust and soot) present in the air will penetrate the paper’s surface or accumulate on a paint

Insects: Silverfish, termites and wood worms can cause considerable damage to paper and canvas.

Varnish: Older paintings, and many modern ones are coated with natural resin varnishes as a protective layer. While the varnish served a purpose, the resin darkens with age and exposure, sometimes significantly altering and obscuring the appearance of the original work.

This painting was executed on raw linen that did not have a proper ground applied. The painting technique also involved the use of a heavy impasto application of pigments. These factors can complicate the conservation process, making the varnish removal more labor-intensive. 

Painting before conservation treatment

Painting before conservation treatment

Painting after conservation treatment

Painting after conservation treatment

Treatment of a Stained and Embrittled 1858 Audubon Chromolithograph

Audubon Wild Turkey with acid staining

Before Treatment: (Above left) The embrittled paper was fragmented about the perimeter. Tide marks from water damage are evident, as well as horizontal stains from the old wooden shingles used to back the original frame.

Audubon's Wild Turkey after restoration

After Treatment: (Above right) To repair the damage, the acidic paper mount was removed and perimeter fragmenting was fiber filled. Staining was chemically reversed and the sheet deacidified by non-aqueous methods.

The conservation process of deacidification can usually arrest or significantly reduce deterioration of artwork, objects, or collectibles made of acidic paper. 

Acid: The Enemy Inside Paper

Certain elements that cause damage are inherent in paper. Consequently, dangers may come from within. Early papers were produced primarily from pulp made of rag (cotton fiber). It wasn’t until the latter half of the nineteenth century that wood-pulp fibers were introduced to commercially produced papers. Lignin, a natural element which bonds the cellular structure in a living tree, becomes an unstable component in ground or emulsified wood pulp, causing an acidic reaction

Envision the strands of paper fibers as links in a chain. Acidic paper loses its strength and the links begin to break down. It becomes brittle and unable to support itself. In addition, wood-pulp paper fibers are short, producing a weaker sheet. Alum-rosin sizing, sometimes added during the paper-making process, also is an acid producer. All acidic paper eventually will deteriorate if untreated.

Use of acid-free (100% rag) paper by publishers and artists is part of the solution. Collectors also should ensure that acid-free mats and papers are used in framing their pictures. If you have an object or collectible made of acidic paper, such as baseball cards, the deterioration usually can be arrested or significantly reduced by the conservation process of deacidification. Also, when paintings are framed to the edge in a wooden frame, the rabbet of the frame that is in contact with the canvas should be lined with an acid-free barrier.

A lithograph by Toulouse-Lautrec darkened by acidity
paper acidity can be reduced through deacidification

A Lithograph by Toulouse-Lautrec Darkened by Acidity

Tide marks from water damage were present and the sheet was improperly laid down on a poor quality acidic paper mount. After treatment, the mount and a damaging animal-based glue have been removed. The weakened paper was backed with an acid-free mulberry tissue. Staining was reversed and the paper deacidified by aqueous treatments.

What kinds of problems can be rectified and how successful can treatments be?

At times, our conservation lab parallels a hospital emergency room. We treat pictures that have suffered everything from floods to bullet holes. The problems we encounter and the dramatic results we can achieve are often impressive.

  • Embrittled paper can be rehydrated and supported with special tissues.
  • Fragmenting and tears can be effectively repaired.
  • Stains resulting from water, pressure-sensitive tapes, glues, mold or mildew (foxing) and rust can be eradicated or significantly reduced.
  • Pieces that have been improperly mounted or glued down to boards can usually be removed from mounts and all glue residue eliminated.
  • Pigments that are cupping or flaking off can be consolidated and stabilized.
  • Varnish, lacquers and shellac can be removed from most surfaces.
  • Folds can be reversed or significantly reduced with controlled humidification and drying procedures.
  • Cockling or waviness from exposure to excessive water or humidity can be reversed.
  • Severely deteriorated canvases can be relined adding support to the canvas and pigment layer.
  • Trimmed canvases can be strip lined making it possible to properly re-stretch them.
  • Torn or punctured paintings can be “rewoven” and pigment losses can be replaced.

The anticipated results are discussed with the client before proceeding with any treatment. Our vast experience with works of art and family heirlooms allows us to accurately predict the degree of success we can achieve. For additional assurance, we frequently secure permission to test a piece before proceeding with any work.

A conservator dry peels a mount from a work of art

Dry Peeling

A paper conservator dry peels a mount from a work of art carefully using scalpels to remove the acidic mount layer by layer.

Paper Conservation & Restoration Treatments – A Case Study

This breweriana poster is severely damaged

Before Treatment: (Above) The recto of the sheet was severely fragmented. Tears and voids had been improperly backed with pressure-sensitive tapes which caused additional staining. Water damage was evident and tide marks were visible throughout; cockling was severe. 

Treatment of a Water-Damaged Antique Breweriana Poster

Before Treatment: (Right) On the verso of the sheet, pressure-sensitive tape had been heavily applied to tears and voids. The sheet was dark from a high acid content. Staining from the old wooden backing was visible.

Verso of unrestored breweriana poster
After restoration the tapes, tide marls, and stains have been reversed
Substantial paper and pigment losses were present prior to restoration

Before treatment: (Detail above) Substantial paper and pigment losses were predominantly in the bottom right quadrant.

During treatment the recto of the sheet was temporarily faced with mulberry tissue to stabilize the poster

During Treatment: (Above) The recto of the sheet was temporarily faced with mulberry tissue to prevent further fragmenting during tape removal. After the tapes and adhesives were removed from the verso of the sheet, it was backed with mulberry tissue and then the facing was safely removed.

After Treatment: (Left and detail above) Pressure-sensitive tapes and adhesive have been removed. Tide marks and pressure-sensitive tape stains have been reversed. The entire sheet was backed with mulberry tissue, voids were completed, and pigment losses were replaced.

Our Philosophy Rests on the Basic Principles of Art Conservation

  • The Principle of Discretion: The first task after examination is to decide whether the object will benefit from active treatment. A vast majority of cases do warrant treatment. There are instances, however, when a passive treatment such as proper archival storage or limiting exposure to ultraviolet light, is the only recommended solution. It is important for a conservator to know when to proceed, and to advise their client accordingly.
  • The Principle of Original Integrity and Allegiance: A conservator’s primary allegiance is to the integrity of the object or work of art and its preservation. An object should not be “over restored”. The artist’s intent, when applicable, should be respected. 
  • The Principle of Reversibility: Technology will change and the knowledge base will undoubtedly grow, therefore all materials and techniques used in the restoration process should be reversible. A future conservator should be able to undo anything that is done today so that the object may benefit from any advancement in the field
Conservators at work in our conservation laboratory

How can I determine that my art or heirloom is valuable enough to warrant the cost of restoration?

Value can be characterized in three ways: monetary, historic, and sentimental. Collectors of fine art, realizing that their collection will survive them, feel they have a custodial duty to safeguard it for posterity. This responsibility applies to family heirlooms as well. Many people possess documents which are important links in preserving family history and memories. Marriage certificates, naturalization papers, deeds, diplomas, letters and antique photographs usually can at least be stabilized in a cost effective manner.

Our staff has the experience and expertise to provide you with an educated opinion relative to the significance or approximate value of your piece. We will not recommend that you restore or conserve something of dubious quality or value. Usually, we can offer more than one option to address your specific needs.

How do I send my piece to you and receive an estimate?

A written estimate and condition report are prepared without charge upon receipt of your object or artwork. If you elect not to proceed with any work, it will be returned to you for a nominal packing and shipping charge. Our shipping and receiving department is dedicated to proper handling and packaging of valuable items.

Our professional and experienced staff can schedule and complete most treatments within a six-week period. Your local professional framer or art gallery can advise you about our service, and is an excellent liaison for shipping and handling of the piece.

To send us your piece, please refer to proper packaging instructions, the printable condition report and client information forms on the restoration page on our website: This information form should be included with your package.

Conservation & Restoration Case Studies

Treatment of an Old Master Drawing

Baldassare Peruzzi before restoration

Before Treatment: (Left) The sheet of this Baldassare Peruzzi 16th-century pen and ink drawing of a design for a frieze had been laid down on a heavy rag mount. There were numerous voids, tears and thinned areas throughout the piece

Before Treatment: (Detail left) The void on the right side had an old paper inlay. Other voids reveal the mount behind, which had been toned.

During Treatment: (Above) After the mount was removed, the piece was viewed on a light table and pre-existing thin areas, tears and voids were revealed.

After Treatment: (Right) A thin mulberry tissue has been applied to give support to the verso of the sheet. New cotton-fiber paper pulp was employed to complete the voids. The new fiber was toned, lending continuity to the composition. 

After treatment, a thin mulberry tissue has been applied to support the artwork

Treatment of a Damaged Antique Asian Screen

Before Treatment: (Detail above) Areas in the sky were improperly inpainted with gold paint and severe tide marks from water damage were visible in panels one and two.

This damaged Asian screen was in need of restoration

Before Treatment: (Above) Numerous previous restorations, some very old, marred the appearance of this six-panel antique Asian screen. Improperly repaired tears were evident throughout. Vertical tide marks damaged the pigment surface and caused staining. Many old repairs and surface abrasions were improperly over painted with gold paint creating an uneven and unattractive overall appearance. The lacquered wooden frame was worn and had been poorly retouched.

The tears were backed during restoration

During Treatment: (Above) To repair tears, the screen was opened from the
back revealing multiple layers of tissue and the wooden armature of the screen.
A heated palette knife was used to activate the archival adhesive to stabilize the tears.

During Treatment: (Above) Previous improper metallic paint applications were removed and new gold leaf was applied to the background where losses had originally occurred.

After Treatment: (Right) Tide marks and water damage have been reversed. Tears were repaired, fiber filled and pigment losses were replaced. New gold leaf was applied in missing areas and toned to match the original gold leaf. The original wooden frame was removed, refinished with black lacquer, and refitted to the screen.

Treatment of a Painting Torn in Half

This painting was torn in half

Before Treatment: This painting was torn in half. The surface was discolored from old natural resin varnish that was also abraded and had associated pigment losses.

During Treatment the canvas was relined to give structural integrity to the brittle canvas

During Treatment: The canvas was relined to give structural integrity to the brittle canvas. Old varnish was removed, and a synthetic fiber was molded into the canvas.

: A mold was taken from the surface of the healthy canvas and pressed into the new synthetic fiber duplicating the weave of the original canvas.

During Treatment: A mold was taken from the surface of the healthy canvas and pressed into the new synthetic fiber duplicating the weave of the original canvas.

During Treatment: Pigment losses were replaced.

During Treatment: Pigment losses were replaced.

The canvas has been re-stretched onto a new stretcher and a non-yellowing synthetic resin varnish was applied.

After Treatment: The canvas has been re-stretched onto a new stretcher and a non-yellowing synthetic resin varnish was applied.

Treatment of a Fragmented Antique Photograph

At some time, pressure had been applied to this antique photograph and caused significant fragmenting and breaks.

Before Treatment: At some time, pressure had been applied to this antique photograph and caused significant fragmenting and breaks.

After Treatment: Breaks have been supported with mulberry tissue. Fragments were completed with new paper grafts. Tears and breaks were fiber filled and pigments replaced.

Treatment of a Torn and Fragmented Document

This document was first damaged by folding.

Before Treatment: (Above left) This document was first damaged by folding. The resultant tears and fragmenting had been improperly mended with pressure-sensitive tapes. A fatty substance in the tape had saturated and severely stained the paper

After Treatment: (Above right) The multiple treatments began with removing all improper repairs, including pressure-sensitive tapes and gum residue. Then, fragments were joined with mulberry tissue using a pH-neutral, starched-based adhesive. Voids were completed with paper grafts and tears were fiber filled. The void completions were then toned to achieve a cosmetically successful solution.

A Lithograph that was Glued to an Acidic Board

A black and white Alexander Hogue lithograph was glued to an acidic board. The animal-based glue evident on the margin had severely darkened with age. To treat the problem, the artwork was removed from the mount. All damaging adhesives were dissolved and removed from both the verso and recto of the sheet.

Before Treatment

A Lithograph that was Glued to an Acidic Board

After Treatment

After restoration, the acidity and adhesives were removed

An Oil Portrait Severely Darkened by Aged Varnish

This early 20th-century oil portrait on canvas was severely darkened by an aged natural resin varnish. Cleaning involved varnish removal and applying a new synthetic resin varnish.

Before Treatment

This painting is darkened by an aged varnish

After Treatment

A Color Photograph with Water Damage to the Emulsion

This color photograph experienced extreme water damage that removed part of the emulsion surface on the left side. Cosmetic restoration involved simulating the emulsion surface and recreating the missing image area.

Before Treatment

After Treatment

Cosmetic restoration involved simulating the emulsion surface and recreating the missing image area.

A Newspaper Damaged by Folding and Moisture

This 1865 newspaper documenting the assassination of President Lincoln had been folded and unfolded repeatedly, causing the paper to break down at the folds. It also suffered from exposure to moisture and humidity. Aqueous methods were employed to flatten the paper which was then backed with a thin support of mulberry tissue. The voids were toned to match the paper tone. 

Before Treatment

A Newspaper Damaged by Folding and Moisture

After Treatment

Aqueous methods were employed to flatten the paper which was then backed with a thin support of mulberry tissue