Influence of the weathering rate on the response of granite to nanosecond UV laser irradiation

Laser ablation is an accepted cleaning technology for cultural heritage stonework. Optimized laser ablation may, however, have different side effects depending on the mineralogical composition of the stone. In the case of granitic rocks, observed side effects - colour changes, fracturing or/and mineral melting - have been attributed to laser parameter interactions with the patina to be cleaned from this complex rock with a grained texture and polymineral composition. We describe the influence of the weathering degree of a granite on its response to laser irradiation, confirming that the existence of secondary minerals in the rock influences the intensity and typology of side effects. Knowledge of this influence is of special relevance to the conservation of heritage built with Western European Variscan granites, which are already slightly weathered in quarry. Two specimens of the same Variscan granite taken from the same quarry but with different colours (suggesting different weathering rates) were subjected to nanosecond (ns) Nd:YVO₄ laser irradiation, working at 355 nm (UV irradiation) under different fluences. The specimens responded very differently to laser irradiation in terms of colour changes and resistance of the main minerals to laser radiation. The existence on one of the specimens of kaolinite deposits covering feldspar grains and Fe oxyhydroxides filling fissures seemed to be the reason for the different response to laser radiation. Our findings would suggest the need, during laser interventions, to take into account - in addition to texture and porosity - the degree of weathering of this particular kind of granite, widely used in the architectural and archaeological heritage of Western Europe.

Effectiveness of granite cleaning procedures in cultural heritage: A review

Most of the Cultural Heritage built in NW Iberian Peninsula is made of granite which exposition to the environment leads to the formation of deposits and coatings, mainly two types: biological colonization and sulphated black crusts. Nowadays, another form of alteration derives from graffiti paints when these are applied as an act of vandalism. A deep revision needs to be addressed considering the severity of these deterioration forms on granite and the different cleaning effectiveness achieved by cleaning procedures used to remove them. The scientific literature about these topics on granite is scarcer than on sedimentary carbonate stones and marbles, but the importance of the granite in NW Iberian Peninsula Cultural Heritage claims this review centred on biological colonization, sulphated black crusts and graffiti on granite and their effectiveness of the common cleaning procedures. Furthermore, this paper carried out a review of the knowledge about those three alteration forms on granite, as well as bringing together all the major studies in the field of the granite cleaning with traditional procedures (chemical and mechanical) and with the recent developed technique based on the laser ablation. Findings concerning the effectiveness evaluation of these cleaning procedures, considering the coating extraction ability and the damage induced on the granite surface, are described. Finally, some futures research lines are pointed out.

Characterization of drying paint coatings by dynamic speckle and holographic interferometry measurements

In this work we implemented dynamic speckle and holographic interferometry techniques to characterize the drying process of solvent-based paint coatings. We propose a simple way to estimate drying time by measuring speckle activity and incrementally fitting experimental data through standard regression algorithms. This allowed us to predict drying time after about 20-30 min of paint application, which is fast compared to usual times required to reach the so-called tack-free state (≈2  h). In turn, we used holographic interferometry to map small thickness variations in the coating surface during drying. We also demonstrate that results obtained from both techniques correlate with each other, which allows us to improve the accuracy of the drying time estimation.

Retinopathy in type 2 diabetic patients with microalbuminuria

OBJECTIVE

To determine the prevalence of retinopathy in type 2 diabetic patients with micoalbuminuria and to evaluate the association of risk factors with prevalence of retinopathy in these patients.

MATERIAL AND METHODS

A fundus examination of 137 patients suffering from type 2 diabetes mellitus with microalbuminuria was done, with direct ophthalmoscope/ binocular indirect ophthalmoscope after dilating the pupils with 1 % tropicamide eye drops. Retinal changes were graded as no retinopathy, non-proliferative retinopathy, proliferative retinopathy and maculopathy. The association of the duration of diabetes, control of diabetes, hypertension, hyperlipidemia, smoking, obesity and peripheral neuropathy was assessed with the prevalence of retinopathy in these patents.

RESULTS

The mean age of the patients was 58 years (range 35 - 79 years); 62 % were females, and 49.6 % were Chinese. Diabetic retinopathy was seen in 36.5 % of the patients - non proliferative in 29.2 %, proliferative in 7.3 % and maculopathy in 5.1 % of patients. A longer duration of diabetes (p = 0.002), poor control of diabetes (p = 0.002), presence of hypertension (p = 0.03), and presence of peripheral neuropathy (p = 0.001) were significantly associated with the prevalence of retinopathy; while hyperlipidemia (p = 0.29), smoking (p = 0.43) and obesity (p = 0.43) were not associated with retinopathy.

CONCLUSION

Retinopathy was seen in 36.5 % of type 2 diabetic patients with microalbuminuria; 7.3 % had proliferative retinopathy and 5.1 % maculopathy (both sight threatening changes). All diabetic patients with microalbuminuria should be screened for retinopathy so that treatment can be instituted in the required patients to prevent ocular morbidity/ blindness.