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Controlling humidity and tarnishing in showcases


I received a reply from one gallery that some of my post on this
subject did not come through. In case this has happened at Orchid,
here is the missing portion again.

My daughter wrote;

"I am not sure in the end if it was caused by the paint or the
wood in the case. All of the wood in the case was supposed to
have been completely wrapped in an aluminum laminate barrier
foil (Marvelseal) but instead the Marvelseal had been applied
up to the cut edges of the wood - leaving the freshly cut edges
of crappy plywood exposed in the sealed case, covered only with
fabric. Also the back of the case was painted with a PVC paint.
That sounds horrible - I may not be remembering correctly - can
there really be PVC paint!?

We do have guidelines and recommendations for the display of
silver artifacts. Attached.

Problems with display cases are: sealed up, not good air
circulation, pollutants/off gassing gets concentrated; any
materials can cause tarnishing: paints; gaskets; fabrics;
woods; fabric finishes etc. Tarnish is accelerated by UV and by
higher temps and RHs. As for paints, I recommend the ones with
low or no VOCs (such as Benjamin Moore Eco-Spec), but we don’t
generally put paint in cases with silver because wood is bad
and you can’t paint Marvelseal.

Guidelines for the safe display of silver artifacts on loan
Objects Conservation
Museum of Fine Arts, Boston

Uncoated silver tarnishes readily in the presence of atmospheric
pollutants. To minimize silver tarnishing, it is preferable to
display silver artifacts in clean, inert environments rather than to
coat or lacquer the metal. Case construction materials, adhesives,
fabrics, labels and gaskets can all be sources of damaging
pollutants. High relative humidity and ultraviolet light (UV)
accelerate tarnish reactions.

General Guidelines:

a… Silver should only be handled with clean gloves and never with
bare hands. If cotton gloves are used, they should not have
"grip-dots." Plastic gloves (nitrile, latex or vinyl) should not be
powdered or otherwise treated.

b… Silver objects should be displayed behind a vitrine with a
locking mechanism, alarm, and/or security screws.

c… Pedestals should be securely fastened to the floor or wall.

d… Lighting sources should be equipped with UV filters.

e… MFA objects conservation may require that desiccating silica gel
be incorporated into the case design to condition air within the
display area, keeping the relative humidity below 45%. If wood or
other organic materials are part of the object, the humidity should
be stabilized at 45%-50%. Humidity indicating strips or other means
of determining the relative humidity in the case should be visible
without opening the case. MFA objects conservation may require that
additional sorbents such as activated carbon, zeolites, or
silvercloth be used.

Case Material Guidelines:

a… Materials used in case construction should be tested and
approved by the MFA Scientific Research division, or another
scientific facility, with test results provided to the MFA, Boston.
Testing requires a minimum of six weeks. Adequate time must be
allowed in the design of cases to allow for retesting if necessary.

b… All wood or wood products (including Medex, Medite II, MDO and
HDO) in the display area must be completely covered with a vapor
barrier laminate such as Marvelseal 470. The display area includes
any area in the case, visible or not, with shared air circulation to
the display area including areas underneath or above the deck. The
Marvelseal should be applied with heat. Some aluminum foil tapes are
also acceptable for sealing gaps or small areas, see below.

a… Alternatives to wood and wood products are: glass, powder-coated
steel, aluminum/polyethylene laminates such as Alucobond,
high-density polyethylene foams such as Ethafoam 900), sheet
aluminum, or other materials that do not offgas. These products do
not require the application of Marvelseal, although wood products
accessible to the display area would still require the application
of a vapor barrier.

b… If paint is used in the display area, it must be tested and
approved by the MFA or another scientific facility, and adequate
drying time must be built in to the installation schedule. The
minimum acceptable drying time is three weeks in a well ventilated
space. Since this is often impractical, the use of fabric over a
vapor barrier such as Marvelseal may be a better choice.

c… Fabric used in cases must be tested for off-gassing and approved
by the MFA or another scientific facility. Washing fabrics prior to
use to remove sizings and fire retardants often improves test
results. Untreated cotton or linen is usually the best option.
Fabric should be applied with staples, 3M 450 double sided adhesive
tape or another non-off-gassing tape, but not with adhesives unless
they are specifically approved by the MFA.

d… Vitrines should be gasketed to maintain a well-sealed case.
Polyethylene, Gore-tex or alcohol-cured silicones are generally
acceptable but also require testing before use. Natural rubber,
latex rubber, polyurethane, EPDM (ethylene propylene diene
terpolymer), and acid-cured silicones should not be used.

e… Label materials should be tested and approved by the MFA or
another scientific facility. In general, archival papers printed
with laser or ink jet printers are suitable, along with acrylic
adhesives and acid-free cardstock. Oil-based inks should not be

A list of materials and suppliers will be provided.
November 2002

Marty Hykin


I have suddenly been having trouble with tarnish on my earrings. Am
I correct in my understanding that this may be because I transport
them in a unfinished wooden box which I designed to hold my display
racks? The tarnish is not black, but makes them look gold.

In case it makes a difference, they are all hand melted and drop