Parks Canada's mandate is to preserve their collections of archaeological artifacts and historic objects in order to extend their physical life and retain their value. This mandate as the topic is too extensive to go into in detail on this website.

The conservation staff of Parks Canada participate in national and international organizations that promote heritage conservation, protecting heritage from loss or from deterioration. They are active in many professional associations: providing direction as members of the executive or special committees, writing publications, and participating in conferences, seminars and workshops.

Their clients are the National Parks and National Historic Sites. In special circumstances there services may be provided to other heritage institutions.

Laboratory Conservation

• archaeological organic objects including basketry, leather, rope, textiles, wood, etc.
• large historic objects such as canons and machinery
• paper objects including books, maps, parchments, manuscripts, prints, drawings, pastels, photographs, etchings, engravings and watercolours
• furniture and furnishings, upholstery and gilding
• reproduction of archaeological and historic textile objects such as clothing, flags, tapestries, and household fabrics
• paintings on canvas, glass, wood, leather, metal and other surfaces
• polychrome sculpture
• archaeological and historic objects of ceramic, glass, and stone

On-site Conservation

• environmental surveys and recommendations for the storage and display of objects
• condition assessment of objects on display and in storage
• conservation support for land and marine excavations
• assessment and monitoring conservation of objects at the site
• preventative and remedial conservation of objects at the site
• presentation of seminars and workshops upon request
• Conservation labs also handle registration, handling, packing and movement of objects

Conservation
The archaeological team is made up of many specialists. Conservators, the people who carry out the conservation of the artifacts, are part of the team. If the excavated artifacts are not preserved properly, scientists and researchers will not be able to study them in later years. In the process of examining and treating objects, conservators bring new information to light about the artifacts that archaeologists recover.

What is Conservation?
Conservation can be described as all actions aimed at prolonging the existence of artifacts with the least possible intervention.
Conservation includes examination, documentation, preventive conservation, preservation, and restoration.

Examination and documentation
Examination under a microscope can reveal detail not visible to the naked eye, for example scratches made when a tool was sharpened, details of inscriptions on coins, or the presence of threads caught in the back of a button. Sometimes high-tech methods are used to examine artifacts. For the Grassy Island material, x-rays were used to determine what exactly was inside the rusty lumps that were discovered. A piece of "mystery metal" from the well on the How Property was examined in a Scanning Electron Microscope and X-ray diffraction was used to find out that it was pure tin.

Preventive Conservation
This is the implementation of optimized conditions for the examination, storage, display and handling of artifacts. During archaeological excavations, conservators advise on methods for keeping artifacts safe until they reach the conservation lab. This includes suggesting the techniques for lifting objects out of the ground in one piece, appropriate containers and soaking solutions.

Preservation
Preservation is both preventive conservation and treatment (or intervention). The goal of treatment is to prevent an artifact from changing. Changes happen when artifacts are excavated from the ground and include things such as shrinkage, corrosion, and damage due to inappropriate handling.

Restoration
Restoration includes modifying the existing form of the artifact to a known, earlier state. For example, reassembling ceramic sherds to form complete vessels. Many of the ceramics on display at the visitor centre in Canso have been restored. Pieces of the ceramic that were missing when it was reassembled were replaced with plaster or resin. The replacements were then painted to match the original, so that visitors can see what the original looked like.

Conservation at Parks Canada
The Parks Canada mandate is to protect and preserve significant examples of Canada's natural and cultural heritage in a sustainable manner. There are Parks Canada Historic Resource Conservation Labs in the Ontario Service Centre (Ottawa), The Prairie and Northern Service Centre (Winnipeg), The Quebec Service Centre (Quebec City) and in the Atlantic Service Centre (Halifax). These labs provide conservation services to the National Parks and National Historic Sites. In special circumstances, their services may be provided to other heritage institutions. Artifacts from the excavations at Grassy Island were treated at the lab in Atlantic Service Centre.

Conservation Treatment of Artifacts from Grassy Island
There were two factors affecting the artifacts at Grassy Island that had to be considered during treatment. Many areas of the site were wet at the depth the artifacts were found, so wood and leather artifacts were waterlogged. The soil also contained salt, so iron and copper artifacts had to be chemically stabilized soon after excavation. Here are two examples of artifacts that were treated after excavation:

The Bucket from the Well on the Howe Property

The bucket was found in the well pictured below. It was well preserved because the clay and water prevented exposure to oxygen, but it was waterlogged. Like other plant materials, wood is made up of cells. Normal wood has a layer of water chemically bound into the cell wall. The cavity of the cell is filled with some water but it is mostly air. When wood is waterlogged, the cells cavities are filled with water. Even if the cell walls are weak, the wood can appear in good shape because the water inside the cells stops them from collapsing. The first step in preserving the bucket was to wrap it in a separating layer of tin-foil, and put it in a cast of resin bandage so that it could be removed from the well without damage. It was then carefully kept wet until it could be transported to the Conservation Lab in Halifax.

What happens if waterlogged wood dries out?
The results can be quite dramatic. When the water evaporates out of the cells, the walls collapse and the wood shrinks. Wood shrinks more across the grain than in any other directions, so the dried wood will be a different shape to the original. When the water that is bound to the cell wall evaporates, the water molecules tug at the cell walls (surface tension) and cause more cell walls to collapse like a pricked balloon.

How can waterlogged wood be preserved?
In treating wood, the aim is to prevent the damage that would happen if the piece were left to dry out. Various techniques and chemicals are used to lower the surface tension of the water, make the wood stronger, fill the cell with material to support it when the water leaves, chemically replace bound water or slow down drying.

The most common treatment is to use polyethylene glycol, or PEG, which can accomplish most of these objectives. One type of PEG replaces the water bound to the cell wall. Another type of PEG replaces the water sitting inside the cells when it solidifies into a hard material. To prevent damage occuring to the bucket when it dried out, it was disassembled and treated with Polyethylene Glycol. The bucket was reassembled and then dried in a freezer.

The photo to the left shows the bucket with the conservation treatment about 80% completed. The split branches that wrapped the bucket and held the staves together are still drying in the freezer. Imagine that this bucket was once used by the soldiers and settlers living on Grassy Island in the eighteenth century. Conservation helps to bring that era back to life.

How does Polyethylene Glycol Work?
Polyethylene glycols are water soluble waxes, commonly used in the food industry as coating for fruits and vegetables. PEGS are made with different sizes of molecules. The shorter molecule varieties come as liquids, and are used in treatment to replace water in the cell wall. The longer molecule varieties come as solids, and are dissolved and used in treatment to fill up cell cavities. It takes time for PEG to soak into the interior of the wood being treated, so wood is left to soak in a solution of PEG and water for up to 2 years. The trick in making up the soaking solution is to use the right concentration of the liquid PEG to replace all the water in the cell wall. If too little is used the cell wall will shrink, and the wood will crack and warp. If too much is used the wood will be difficult to dry, and even when dry will be dark and waxy in appearance.

With small artifacts of wood, finding the right concentration is easy. The density of wood can easily be calculated from buoyancy (flotation) measurements and compare that density to the average density of its' species. This tells how degraded the wood is. A computer program can then be used to determine exactly how much cell cavities remain. The computer then calculates the exact amounts of PEG needed to replace the water and fill the cells. After soaking the artifact is dried in a freeze drier. This results in a object that looks natural, and doesn't shrink during the process.

With very large artifacts, it is difficult to measure the density. The bucket found on Grassy Island was in very good shape bescause it was protected by the clay and water from exposure to oxygen. The photo to the left shows the final product after conservation. Imagine that it was once used by soldiers and settlers in the early 1700's. Conservation helps to bring that era back to life.

Conservation is one of the most important aspects of archaeology. If the artifacts found are not preserved properly, scientists and researchers who wish to study them years later will not be able to.

The Watch Fob

The watch fob was excavated from well drained soil around the How Property. The surface was covered with corrosion products because the water, oxygen and salt in the soil enabled the metals to corrode easily. The watch fob was made of iron or steel with copper alloy decoration but because iron corrodes in preference to copper when the two metals are in contact (Galvanic Corrosion) only iron corrosion was visible.

The corrosion on the watch fob was removed using an abrasive powder (aluminum oxide) in a small sand blaster. A microscope was used to magnify the artifact when it was being treated. This prevented the possibility of damaging the surface of the artifact. It was only after the iron corrosion products were removed, that the copper alloy decoration became visible.

Iron is very susceptible to corrosion and this watch fob was no exeption - it continued to corrode, even in the lab. In order to hold the artifact together, an epoxy resin was dripped into the cracks. Under normal circumstances, conservators do not use treatment techniques that cannot be reversed but when there is a risk of losing the artifact altogether, exceptions can be made.

If iron corrodes so badly, how can iron artifacts be preserved ?

When iron artifacts are excavated from land sites, they are usually a little damp. The requirements for corrosion, water, oxygen and salts, are always present. So conservators have two options: they can remove the water from the storage environment by using a drying agent such as silica gel; or they can remove the oxygen. The second option is achieved by immersing artifacts in water. Some corrosion occurs but the reaction stops when all the oxygen in the water is used up. There is an added advantage in that some salts are also removed.

When the artifacts are treated, they are returned to the archaeologists for further study. It is important that as much information as possible be recorded because, even in the best storage conditions, iron artifacts always remain unstable.

SOURCE: Colleen Day, Maureen, and Parks Canada Staff at Conservation Lab, Burnside, Dartmouth Industrial Park, Halifax, N.S.