LESSON 9 Flashcards
Modification of the material that does not necessary imply a worsening of its characteristics from the point of view of conservation.
alteration
Human perception of the loss of value due to decay.
damage
chemical or physical modification of the intrinsic stone properties leading to a loss of value or to the impairment of use.
decay
Decline in condition, quality, or functional capacity.
degradation
Process of making or becoming worse or lower in quality, value, character, etc.; depreciation.
deterioration
Any chemical or mechanical process by which stones exposed to the weather undergo changes in character and deteriorate.
weathering
Individual fissure, clearly visible by the naked eye, resulting from separation of one part from another.
crack (fissure)
crack sub types:
- fracture
- star crack
- hair crack
- craquele
- splitting
Crack that crosses completely the stone piece
fracture
Crack having the form of a star. Rusting iron or mechanical impact are possible causes of this type of damage.
star crack
Minor crack with width dimension < 0.1 mm
hair crack
Network of minor cracks also called crack network. The term crazing is not appropriate for stone, as this term should be used for describing the development of a crack network on glazed terracotta
craquele
Fracturing of a stone along planes of weakness such as microcracks or clay/silt layers, in case where the structural elements are orientated vertically.
splitting
Change in shape without losing integrity, leading to bending, buckling or twisting of a stone block.
deformation
Separated, air-filled, raised hemispherical elevations on the face of stone resulting from the detachment of an outer stone layer. This detachment is not related to the stone structure.
blistering
Local loss of the stone surface from internal pressure usually manifesting in the form of an irregularly sided crater.
bursting
is sometimes preceded by star-shaped face-fracturing.
bursting
loss of material due to a mechanical impact, which may have crater shape if the object hitting the stone surface is hard and small (a bullet for instance).
impact damage
Detachment process affecting laminated stones (most of sedimentary rocks, some metamorphic rocks). It corresponds to a physical separation into one or several layers following the stone laminae.
delamination
delamination sub type:
exfoliation
kind of detachment totally independent of the stone structure.
scaling
Detachment of single grains or aggregates of grains.
disintegration
detachment of multiple thin stone layers (cm scale) that are sub- parallel to the stone surface. The layers may bend, twist in a similar way as book pages.
exfoliation
disintegration sub types:
- crumbling
- granular disintegration
Detachment of aggregates of grains from the substrate. These aggregates are generally limited in size (less than 2 cm). This size depends of the nature of the stone and its environment
crumbling
Occurs in granular sedimentary (e.g. sandstone) and granular crystalline (e.g. granite) stones.
granular disintegration
produces debris referred to as a rock meal and can often be seen accumulating at the foot of wall actively deteriorating.
granular disintegration
The following specific terms, all related to granular disintegration, refer either to
the size, or to the aspect of corresponding grains:
- powdering or chalking
- sugaring
- sanding
terms sometimes employed for describing granular disintegration of finely grained stones.
powdering or chalking
employed mainly for white crystalline marble.
sugaring
used to describe granular disintegration of sandstones and granites
sanding
