The results of discoloration mapping are summarized in Table 6.1 below, and the comparisons were made in chart 6.1.
Facade name
Discoloration stage (%) Percentage
of discolored
stones
non slight moderate High
Western 50.80 % 14.50 % 27.05 % 7.56 % 49.20 %
Southern 45.79 % 16.19 % 30.44 % 7.58 % 54.21 %
Eastern 42.19 % 6.29 % 18.38 % 33.13 % 57.81 %
northern 31.49 % 18.08 % 34.75 % 15.67 % 68.51 %
Average 42.57% 13.77% 27.66% 15.99% 57.43%
Table 6.1 discoloration stages percentages
Chart 6.1 comparisons of discoloration stages percentages
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From the mapping results above, the highest percentage of discolored stones from all stages was found to be in the northern side by 68.51%, followed by the eastern side (57.61%), by the southern side (54.21%) and the lowest percentage was in the western side by 49.20%. the average of discolored stones from all stages and for the whole building is 57.43%, in other words, an average of 57.43% of Saint Nicholas Cathedral stones have lost there original colors.
Western façade (figure 6.1) has the lowest percentage of discolored stones compared to the other sides. Very close to the average, the moderately discolored stones have the highest portion between the other stages in this façade, as result of the accumulation of dirt and dust on the surface of stones especially around the three doors.
The southern façade percentage of discolored stones is very close to that at the western façade. The moderately discolored stones has the highest percentage of (30.44%), as a result of tow reasons, first; the accumulation of dust in the presence of the sliding water at the surface of the walls which wash the dirt and dust from up to down, the second reason; is the effect of salts which comes with sea breeze that effect can be noticed on the right side of this façade. Note: cars which passing over the road along this façade releases gases which causes pollution that aids on the process of stone discoloration.
At the percentage of 68.51% the northern façade tends to be the most discolored façade, This very high proportion of discolored stones can be explained by knowing the fact that this side gets less amount of sunlight compared to the other sides (see figure 4.3 in chapter IV), the natural result of this fact is the increase of the percentage of humidity and the moisture content inside and on the surface of the stones, thereby the increase of
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the incidence of chemical reactions and the biological growth of all kinds, both contribute a turn in changing the original color of the stone.
While the northern façade has the highest percentage of discolored stones, the eastern façade has the highest percentage of the highly discolored stones; the main reason behind this maybe is the chemical weathering, more specific the salt weathering which changes the chemical properties of the stone, and one of them is color.
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