- Slabs / tiles should be sorted to ensure uniformity
of shade. Normally, any colour can be sorted into three
shades. Sorting is simple -just lay all the material
on the floor and look from different directions.
If you will buy the entire quantity over a period of time,then
you should make it a point to know from which specific
quarry the material will be supplied as there will always
be a difference between quarries.
Grain variation - If grain varies between
fine and coarse, such tiles / slabs should also be sorted
uniformly by grain size. Sort this the same way as
for shade. The further you see it from, the easier it
is to sort.
Oiling - Many black granites are light
blacks.To make them temporarily look better (blacker),
industrial oil is rubbed on it after polishing.This oil
evaporates after some months leaving the slab looking
very shabby. A burning match will heat an oiled surface
and the oil will rub off on your finger.
Colouring - Similarly, red oxide is
put on red granites to make them look redder and to fill
cracks. To check this, rub the surface hard with your
finger and see if some red colour rubs off. By wetting
the sawn surface(back side of polished piece), you can
see the true colour and nature of any granite.
Colour patches - These are darker or
lighter patches or bands of single colours due to mineral
localisation; in black this occurs as "oil patches"-patches
which look as if oil has been spilled. These are actually
permanent patches. Pay less for such materials.
After laying and seeing from different angles, it
is easy to see which pieces have these defects.
Tapping with your finger nails or spoon may give different
sounds on these patches compared to rest of the granite.
Double colour - Sometimes two different
grain sizes occur in the same slab, giving the appearance
of a double colour. Pay less for such materials.
Cracks - Test by pouring water,
wiping and letting dry. Water which goes into a crack
Staining - Many granites stain. Test
before buying with wet spices or oil kept on it for a
few minutes. Even if staining is not your worry,
if you are going to wash the surface frequently, then
check how long tap water remains absorbed. Some granites
change colour when wet compared with when dry. Since drying
is a slow process, the surface looks unattractive during
the interim period when part of it is wet and part is
Holes - Some crystallic granites do
not have a smooth surface. The surface chips or there
are pin-holes. Avoid this type for horizontal applications.
Having decided on a particular granite, it is important
to note that shade and grain should be uniform in the
entire lot and there should be no colour patches. Do not
accept anyone saying that "this is not possible because
granite is a natural material". If entire material
is from one quarry, it is a simple matter.
Accept defects only to put in hidden places.