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Field
conservation and preservation
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Stabilizing a ceramic during lifting in the field. Photograph
courtesy of Jessica Johnson.
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In situ
or on-the-spot conservation of archeological materials can be an essential
aspect of a field project and can significantly affect the long-term
preservation of objects in the resulting collection. The conservation
and preservation care that an object receives in the field may be the
only care it ever receives. Similarly, all the records produced in the
field, including field notes, maps, photographs, standardized forms
such as site forms, artifact catalogs, audio tapes, and a variety of
digital data, must be created, managed, and handled with care in the
field and lab.
Archeologists should
consider and practice some basic principles and methods of conservation
at all times. On a large site or one where there is likely to be a wide
range of complex conservation needs, it is preferable to have a professional
conservator on site.
Material Remains
An archeological object in the ground is in a state
of equilibrium with, or is adapting to its surroundings when found (Sease
1994). When it is taken out of the ground and exposed to air and different
temperature and humidity levels, that equilibrium is disturbed. The
object immediately begins to react to the changes in ways that are both
visible and invisible to the archeologist. Most often these changes
are in the direction of object deterioration. Planning for conservation
in the field is therefore essential for the long-term preservation of
archeological objects through condition assessment and appropriate actions.
When planning for field conservation needs, it is important to consider:
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The kinds of material remains anticipated;
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What types of conservation treatments may be needed in the field;
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Volume and kinds of archival quality storage materials that will be
required to transport the collection from the field to the lab or
repository;
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How the material remains can best be collected to facilitate their
long-term preservation.
The type of soil
in which objects lie can be used to anticipate the condition and conservation
needs of the recovered objects. Below is a chart that outlines the general
preservation of objects in some basic types of soil conditions. Alkaline
soils have a pH above 7.0 and are most
common in arid climates where evaporation exceeds precipitation. Acidic
soils, with a pH below 7.0, usually occur in areas of high rainfall
and low evaporation. They are also found in areas where there has been
an incomplete breakdown of organic materials in an anaerobic environment
(e.g., peatbog). Saline soils contain a preponderance of salt. They
are usually found in areas that have been inundated by seawater, but
can also be created by human objects and actions (e.g., deterioration
of metal objects; concentration of waste matter or wood ash). Crystallization
of the salt in the soil can occur in areas where evaporation exceeds
precipitation.
Soil Type (adapted
from Sease 1994) |
|
Acidic |
Alkaline |
Saline |
Water-
logged Acidic |
Water-
logged Alkaline |
Desert |
Arctic |
Ceramics |
R-calcar-
eous fillers dissolve |
P-basic structure affected |
P |
R |
P |
G-wind erosion possible |
G |
Lithics |
G |
G |
P-soluble salts |
P |
P-insoluble salt encrus-
tation |
G-wind erosion possible |
G |
Glass & Glazes |
R-alkali leaching |
P-basic structure affected |
P |
R |
P |
G-wind erosion possible |
G |
Wall Plaster |
P |
G |
P |
P |
P |
G |
G |
Shell |
P |
G |
P-soluble salts |
P |
P |
G |
G |
Metals |
|
|
|
|
|
|
|
Iron |
P-
corrosion |
G |
P-
corrosion |
G |
G |
G |
G |
Copper Alloys |
P-
corrosion |
G |
P-
corrosion |
G |
G |
G |
G |
Lead |
P |
P |
R |
G |
G |
G |
G |
Silver |
P |
G |
G-slight saline
P-high saline |
G |
G |
G |
G |
Organics |
|
|
|
|
|
|
|
Bone, Ivory, Antler |
P |
G |
P-soluble salts |
P |
P |
G |
G |
Wool, Leather, Hair |
deter-
ioration of protein |
P |
R-dehyd-
ration |
G |
G |
G |
G |
Wood, Cotton, Linen |
P |
P |
R-dehyd-
ration |
G |
G |
G |
G |
G=good preservation
R=reasonable preservation
P=poor preservation |
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While the conservation
needs of different classes of material remains differ, there are a few
key principles that should be followed in the field to help ensure proper
conservation of all materials:
- Choice of excavation
tools affect the materials and condition of an object. Determine the
best tools that will inflict the least harm prior to field work.
- A number of factors, such as water, temperature,
humidity, and sunlight, affect the stability of an object in the ground
during and directly after excavation.
- Always immediately
cover up an object or a group of objects that seem unstable. Contact
a professional conservator for advice on in situ treatment
and methods to remove the object(s).
- Objects should be kept in bags or containers with
like materials. Improper mixing can cause damage to some objects (e.g.,
placing bones or soft ceramics in containers with large and heavy
lithics).
Field conservation
measures can range from simple, common sense activities to complex procedures.
The following are some general guidelines for conservation in the field.
Remember that any procedures applied to an object should be reversible
-- they can be later be removed without any damage to an object and
its constituents. A professional conservator should always be consulted
for complex treatments or if there are any questions about correct conservation
procedures. In particular, be sure appropriate adhesives and consolidants
are selected.
Handling
- Always assume
an object is fragile. The true condition of an object may not be immediately
apparent.
- Handle objects
as little as possible. Do not pick up objects by handles, rims, or
other attachments.
- Avoid bending
flexible objects.
Lifting
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Physical support created for lifting delicate bone in the
field. Photograph courtesy of Jessica Johnson.
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- The method chosen
to lift an object out of the ground depends on its strength, size,
weight, composition, and condition, as well as the condition of the
soil matrix.
- Assess the object
condition, then record information, sketch and/or photograph the object
before lifting it out of the ground.
- Remove as much
dirt surrounding an object as possible before removal. Do not flick
or pry an object out of the ground.
- Support the
object at all times. A pedestal of dirt may be left underneath the
object for support while continuing to excavate around it.
- Lifting an object
out of the ground with its surrounding dirt (block lifting) is useful
for extremely fragile objects. The appropriate method of block lifting
depends on the size and weight of the object and on soil condition.
Bandaging and
Consolidation
- A bandage can
be used to support fragile objects once they have been excavated.
A bandage consists of gauze or cloth strips wrapped around an object
in layers. Adding plaster or resin can strengthen the bandage, but
do not glue or plaster a bandage directly to an object. It is critical
to apply a separate layer between the bandage and object.
- Backing an object
is useful for fragile, flat objects. Backing
usually involves the application of a rigid bandage to the object.
Some PVA emulsion, Acryloid
B72, or plaster can be used for rigidity. Do not use Elmer's Glue-AllŪ.
- Consolidants
should only be used when absolutely necessary and in consultation
with a professional conservator. The choice of consolidant will depend
on the type and condition of the materials involved. Consolidation
should not be attempted on waterlogged materials.
- Consolidants
can be applied to fragile objects to join pieces and allow for lifting
and handling. Consolidants should have: 1) good adhesive and cohesive
properties; 2) achieve good penetration; 3) be durable, stable, and
reversible; and 4) not alter the appearance of the material consolidated.
- Do not consolidate
any material that will be used for dating or scientific analysis.
- Clean an object
thoroughly before applying a consolidant. The most common consolidants
are PVA emulsions or resins and Acryloid B72. Allow the consolidant
to dry completely before lifting the object out of the ground.
Records
|

Mapping a dog burial in
the field. From the photograph collection of the Bureau of
Land Management, Anasazi Heritage Center, Dolores, Colorado.
|
The records created in the field, as well as in the lab, are vulnerable
to insects, vermin, mold, humidity, light, temperature changes, and mishandling.
They are also vulnerable to a variety of environmental threats, such as
roof leaks, flooding, fire, and asbestos problems, and to theft or other
malicious action.
There are a number
of general recommendations to follow in the field and lab in order to
promote the long-term preservation and viability of the great variety
of records created:
- use appropriate
long-lived media for all record types;
- use permanent
and archival stock in paper, ink, lead pencil, folders, and boxes;
- inspect and
redo damaged or inadequate records;
- label everything,
or their containers;
- use appropriate
storage for all media in the field in order to protect them from poor
environmental conditions and threat of fire or theft;
- carefully consider
existing guidelines and equipment for digital and audiovisual media,
make sure backup copies and hard copy printouts exist, and migrate
data to updated software on a regular schedule; and,
- ensure that
project information and data is captured by appropriately knowledgeable
staff.
There are also a number of conservation principles to consider for each
of the primary types of media used for associated records.
Paper records
- Use high alpha
cellulose, lignin free, acid-free
paper, especially for field notebooks and standardized forms.
- Record information
using archival (permanent carbon) inks or #4 (HH) pencils.
- Protect paper
from water and humidity, and minimize its exposure to light.
- Try not to fold
or roll paper.
- Store papers
in archival folders in polyethylene
boxes.
Photographs
- Protect all photographic
materials (e.g., film, prints, slides, negatives, and transparencies)
from heat, rain, and wind. Store them in archival folders in polyethylene
boxes.
- Maintain a log
of all photographic images.
- Only handle
photos along their edges. Do not touch the image with bare fingers.
- Do not use paper or plastic clips, rubber bands,
pressure sensitive tape, adhesive or pressure sensitive labels, or
Post-itŪ notes directly on photographs.
- Do not put photographic
materials, except unused film, in cold storage without reformatting
them for access and duplication.
Magnetic Records
- Protect all
magnetic materials (e.g., audio tapes, video tapes) from heat, dust,
and dirt.
- Consider the
equipment required to play the audiovisual material and the longevity
of that equipment.
- Label all records
in a permanent, carbon-based ink.
- Store the records
in their cases in polyethylene boxes.
Cartographic and
Oversized Records
- Oversized records should be stored flat in folders,
preferably in map cases. Do not roll or fold.
- Protect paper
from water and minimize its exposure to light.
- During storage
and use, protect oversized records from tears and rips. Do not use
tape to repair tears.
- Label the oversized
folders in permanent, carbon-based ink.
Digital Records
and Data
- Produce your
master records in uncompressed TIFF format, if possible. Avoid using
proprietary file formats or lossy
compression.
- Protect all
digital records from heat, dust, dirt, and ultraviolet radiation.
- Choose a storage
medium that is considered a standard. Research its longevity.
- Keep digital
records away from magnetic or electric fields that are created by
old telephones, static, and field and lab equipment such as magnetometers
and 12 volt transformers. Computer diskettes can be partially or completely
erased by such exposure.
- Label the records
in permanent, carbon-based ink.
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Home
Contents
1.
Introduction
2.
Introduction to Curation
3.
Relevant Laws, Regulations, Policies, and Ethics
4.
Today's Key Issues
5.
Curation Prior to the Field
6.
Curation in the Field and Lab
Field collection
Field conservation & preservation
Lab
sampling & management
Lab conservation
Quiz
Bibliography
Links
Print
this section 
7. Repositories
8.
Collections Management
9.
Access and Use
10.
The Future
Course Certificate
Glossary
Credits
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