Influence of the Laser Wavelength on Harmful Effects on Granite Due to Biofilm Removal

Round 1

Reviewer 1 Report

The paper provides interesting research on an influence of the laser wavelength on granite during cleaning process e.g. due to biofilm removal, however used methods were applied to rock cleaning before. The construction of the research targets, methodology, way the research was performed is very good and I have no claims. Also the results are interesting and discussion on them can be very useful for monument cleaning and restoration. The subject fits perfectly to the journal subject. But I am petrologist and mineralogist and I am offended by generalizations that are not consistent with the processes observed during the formation and degradation of minerals / rocks. They are stimulated here artificially, but I think that the terminology should refer to the mineralogical and petrological sciences. Laser ablation causes material evaporation. The material is heated by the absorbed laser energy and evaporates or sublimates. If we think about mineral material melting we assume that the melt remains in situ. You don’t observe any melt. You observe loss of material due to an evaporation caused by the laser beam. At many places you define the evaporation as a plane melting. Plane (surface) is a flat figure. Biotite is a phyllosilicate composed of flexible sheets. It is also called sheet mineral. So if some parts of the mineral are removed these are not planes, but sheets. I assume that you used terminology used in previous works, but granite is natural rock having natural minerals (with well-defined structures and textures), and the description with use “melting” or “melting of planes” doesn’t fit to natural petrological processes undergoing under high temperature, even if the source of HT is laser and not natural heating provided by crust or mantle.

Author Response

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Reviewer 2 Report

The paper presents experimental results that can be useful for conservation purposes.

There are some data, some results and the methodology is described.

I think the paper falls into the scope of the journal.

I think the manuscript would benefit from a better presentation of the results, in a way to support the discussion. These two parts need more separation. The discussion should probably be more focused on explaining, not stating, the variations of the effect of the laser with the various parameters tested (why does the wavelength have an influence?). In its present form the paper explains very little of the reasons of these empirical results.

I also have a concern about the color change. The minerals have very contrasted colors, but yet the authors consider the general (yellowish-brown) colouration of the rock. It would be useful for the reader to detail the coloration of the minerals and discuss the color change grain to grain when the kaolinite coating has been removed with regard to the general colouration.

I would also suggest to state more clearly a few points:

- What is the exact origin of the granite sample? Has it been polished?

- please avoid the use of acronyms without prior definitions

- a small § describing how ND:YAG lasers work would be useful. Otherwise the paper only targets specialists

- the introduction presents the advantage of using a ND:YAG laser instead of a ND:YVO. But it is very empirical. The reader is not provided with the sufficient information for understanding why the effect on the material can be different.

- L102: “froming” -> forming

- L126-127: does the reference provided gives the porosity of this precise granite? Please state it more clearly in the text as the reference is a general recommendations manual. Furthermore, do the two samples, the one used in 1980 by the PEM commission and the one used in this study, have the exact same provenance? If this is not clear, the open porosity of the sample used should probably be quantified. Granite plutons can show porosity variations and, more importantly, the slab used here has been submitted to natural alteration. The formation of the kaolinite crust may have, in turn, increased the porosity. Please discuss this point.

- L198-199: “4000-400 cm-1 region, with 4 cm-1 resolution”. Why? Please explain or justify this choice.

- L366 to 381: should rather be in “results” than in “discussion” 

Best Regards

Author Response

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