Method and requirements | Procedure | Resource implications | Comment |
---|---|---|---|
Photography Digital camera, tripod | Digital colour photographs, of each exposed face. Change visually quantified using grid overlay | Financial: low—basic equipment. Human: low-medium—taking, assessing and archiving digital images. No expertise required | Low tech, comparison will be visual and somewhat subjective |
Average surface roughness (Ra) surface characterization tool e.g. Diavite or Surtronic. Industry standard settings used = Lt 4.80 mm trace (sample length) and Lc 0.8 cut off filter (does not measure wavelengths > 0.8 mm) | The profile of the surface is measured using a stylus, magnified through software and quantified as roughness average (Ra) in µm, accurate to 0.01 mm Average taken from 10 profiles on each exposed face | Financial: medium—equipment cost approx. €3000 Human: medium—taking 50 measurements/cube is time consuming however very little post-measurement processing is required, no expertise required | Highlights changes in surface characteristics, e.g. smoothing or roughening Standard deviation in the Ra measurements can be used to indicate homogeneity of the surface Cannot be used on very weathered stone or over large lichen growths |
Colour meter/spectrophotometer Ultra Scan Pro USP1577 Hunter Lab. Mode #3 RSEX or similar | Values for brightness (L*) redness (a +) and yellowness (b +) are taken. Average values are calculated from the five points by the spectrometer | Financial: medium–low—from €3000 to buy, the project initially used borrowed equipment at a food science lab. Human: low—spot readings can be taken rapidly and processed immediately by software, no expertise required | Colorimetry has successfully been used as a measure of biomass on stone [ [15], [16] ]. Visual examination must accompany this assessment |
Callipers Vernier callipers | Digital Vernier callipers. Measurements taken in three dimensions (width, depth and height). Three measurements taken in each case. | Negligible—low cost equipment, low human resources—rapidly completed by non-expert | Produces quantifiable measurements but of low accuracy (± 0.1 mm) Margin for human error (established from repeat measurements) is ± 0.3 mm |
Weight Digital laboratory scales (measure to 0.00 g). | Demounted stones (including internally fixed nut) weighed in grams. Stones must be dry before weighing. Calibrate scales | Financial: low—scales from €250 to buy Human: low—quick to take measurements, no expertise required | The requirement for drying the stones can delay this method of assessment for several weeks after demounting |
3D profile scanning Renishaw Cyclone Series 2 SP600 M machine or similar. Used Tracecut programme NB this method was utilized in the initial phase but not for repeat measurements | Profiling done in Z plane in increments of 5–10 mm (i.e. profiles taken at 45, 40, 35, 30, 20 and 10 mm from base). Profiles stored as DXF lines and arcs in CAD | Financial: high—cost of equipment prohibitive unless can access within an institution Human: high—time consuming to take measurements and to process and requires expertise | The measurements could be introduced into CAD software to compare profiles over time, quantify change and produce visual overlays that show the progression of loss |