Series editors' preface - Wood Tools

candle 1900 K
Household electric light bulb 2800 K
Tungsten photographic
studio lamps 3200 K
Tungsten halogen lamp up to 3500 K
Sun 10° above horizon in
clear sky 4100 K
Mean noon daylight 5500 K
Electronic flash 5600 K
Zenith sun (in clear sky) 6200 K
Overcast sky 6500 K
Clear blue sky 15 000–
30 000 K
As far as possible light should be of single
colour temperature as films do not cope well
with light of mixed colour temperature.
Museum galleries are bad in this respect
because of mixed lights and glass (unwanted
reflections) and lack of possibility for control.
Colour temperature meters exist but not for
mixed light sources. Films are available for
daylight, for tungsten and for fluorescent lighting.
Colour correction filters are available and
are especially useful for daylight/tungsten conversion
when moving between indoor and outdoor
shots on one film. When it is necessary to
work in daylight with film intended for artificial
(tungsten) light, an 85B filter can be used
to prevent the pictures coming out blue.
Diffuse lighting such as that from an overcast
sky or fluorescent tubes will illuminate the surface
of an object more evenly than light which
comes from a single point such as spotlight,
rising or setting sun. It is from the contrast of
shadows and highlights that detail is perceived.
Hence diffuse light sources will usually not
show detail as well as light that has a more
directional component. On the other hand light
that comes from a spot source may give rise to
reflections on certain types of surface. It is
therefore necessary to select the type of lighting
appropriate to the type of object and
record required. If an object is illuminated
slightly more strongly from one side than the
other slight shadows will be cast that will give
a more three-dimensional quality to the surface
and allow elements of form or surface detail to
be more readily appreciated. Any difference in
the intensity of illumination from one side or
the other can be judged by the length and
direction of the shadow cast by a pencil held
upright with its base in contact with the sur-
Conservation preliminaries 403
face. This is particularly useful when setting up
copy stand photography for flat objects. It may
be difficult to illuminate some objects, e.g.
carving with deep hollows as evenly as one
would like, and though there are ways of
reducing contrast through selection of film and
aperture settings, it may sometimes be necessary
to deliberately select shadow or highlight
areas and expose accordingly. When lit directly
from above, the hills and valleys of a surface
will be illuminated more or less evenly (hence
the flat appearance of landscapes taken at
noon). As the angle of the light is lowered the
degree of contrast between low and high spots
increases (e.g. autumn afternoon light picks
out details of every pebble on a beach or stone
on a ploughed field). To get the desired result,
lighting may therefore need to be adjusted
both for intensity and direction (and hence also
position). It is useful to remember that intensity
varies inversely with the square of distance.
In other words, halving the distance
from light source to object will reduce illumination
to a quarter.
Daylight is the best light source but if the
object cannot be taken outside there may be a
problem getting enough of it. Electronic flash
or floodlight of correct colour is good choice.
Electronic flash is about right for daylight film.
It corresponds closely in characteristics to daylight
at least as far as daylight films are concerned.
The length and hazard potential of
cable runs should be considered when using
floodlights. Indoors, use of daylight will result
in long exposures (e.g. of 1 ⁄2–1 second) given
the small apertures that are often necessary to
obtain the required depth of field when taking
photographs of objects at close range.
Preferably the camera should not be hand held
for exposures under 1/60th sec though it may
be possible to get away with 1/30th sec exposures
if desperate. The ideal solution to keeping
the camera steady is to use tripod – which
should have pan, tilt and swivel head. This
should be available in the studio or workshop.
In other circumstances exposures of several
seconds can be managed (assuming a small
format camera is being used) with the uncased
camera held flat against some solid and flat
part of a building, radiator, table or floor. If
nothing else is available squatting with elbows
on knees, heels firmly planted on floor can be
good for exposures up to 1 ⁄2 second. When