6th World Conference on NDT and Microanalysis in Diagnostics and Conservation of Cultural and Environmental Heritage, Rome, 1999 May. Published by AIPnD, email: aipnd@numerica.it

TABLE OF CONTENTS

Abstract Introduction Materials and methods Results Conclusions Acknowledgement References

Abstract

The current pervasive preoccupation for the recovery of our cultural heritage has made it desirable to recur to new techniques whose main characteristic is their non-destructive nature. A further advantage of some of these techniques is the possibility of applying them in situ.

On the occasion of the recent restoration of the main portal of a XVIIth century church in a small village near Granada (Spain), we carried out a complete characterisation of the bioclastic calcarenite used in its construction. This determination covered its compositional, textural, structural and physical-mechanical characteristics. Techniques employed included petrographic microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) with spot EDAX analysis as well as various hydric and mechanical tests. All of these destructive procedures required the extraction of greater or lesser amounts of material from the portal of the building.

The state and form of the weathering was also determined, as well as the causes producing the deterioration, most directly or indirectly related to water: rising by capillarity, freeze-thaw, hydric expansion, salt crystallisation, etc. Based on these data, we decided to undertake certain steps for the consolidation and protection of the edifice. Diverse products (organic, inorganic and silica-organic) and methods of application were tested on samples of the same stone type from the historic quarry originally used. Evaluation of the effectiveness of the distinct products was carried out using some of the afore-mentioned techniques and tests (changes in hydric parameters, weight increase, depth of impregnation by SEM, surface hardness, and accelerated aging tests in the laboratory). In addition, we used ultrasound wave propagation (Vp) which, apart from its non-destructive nature, allowed us numerous repetitions in the measurements, great speed in data acquisition, efficiency and low cost.

Data from the ultrasound technique were found to be very similar to those from the other techniques employed. Therefore, we conclude that ultrasound wave propagation is of great interest in the follow-up of treatment applications for the conservation of stone given its non-destructive procedure and many other advantages.

Introduction

The combined use of both destructive (DT) and non-destructive (NDT) techniques for the analysis and evaluation of ornamental stone has seen a tremendous surge in recent decades. The application of NDT, in particular, is viewed more and more as the best option for the evaluation, diagnosis and follow-up of weathering problems and the subsequent preservation of ornamental stone. Nonetheless, on many occasions there is a lack of data allowing DT results (in general more precise and more widely used) to be extrapolated to cases in which NDT is mandatory (i.e., in-situ or inside a building). One of these cases is in the follow-up of the effectiveness of a treatment including protection and/or consolidation. While this is relatively easy to evaluate in the laboratory with the joint use of DT and NDT, the extrapolation of these data for the exclusive use of NDT in situ on the building being treated is not necessarily straightforward. The aim of the present work is to demonstrate how to use DT and NDT ultrasound wave propagation measurements to determine the degree of weathering in a material and to appropriately evaluate the effectiveness of various conservation treatments in the laboratory (using quarry materials). Thus, the usefulness of any particular treatment (the one with the best laboratory results) can be evaluated in the building itself using only NDT (i.e., ultrasound).

Materials and methods

Fig 1: Church facade. Note the high level of decay.

A XVIIth century church in the province of Granada, Spain, was chosen for the study. This church consists of a complex of great architectural simplicity, built using ashlars. The northern face is predominantly travertine stone, while the southern face is dominated by "piedra de Asperón" (bioclastic calcarenite), which is softer and easy to work. Both are from quarries near the church. The only decorative elements are found in the Sol Portal and in the Lonja Portal, which is the object of this work (Fig. 1).

The Lonja portal, 1612, is Renaissance and comprises two parts. The lower section is a rectangular linted capped by a half-point arch and flanked by two columns backed against the wall. The columns consist of a base comprising approximately a third of the height of the column, ending in mouldings both in the upper and lowermost parts. The shaft, which is cylindrical, narrows from the base towards the capital. It is not a single piece, comprising rather ashlars and decorated with striations and flutes. The column is crowned by a Corinthian capital. Resting on the columns is a entablature composed of horizontal cornices with inscriptions. Above the entablature there is a type of flowery decoration. The upper part of the portal is smaller and is crowned by a statue. It lies directly over the entablature of the lower part. The upper section is of practically the same architectural design, but in this case is capped by a pediment.

The church is located in an area of low pollution, but with a warm, dry climate in the summer and a cold, damp autumn-winter, with frequent frosts, dew, and hard rains (Rodríguez-Navarro, 1998). Various types of weathering can be observed in the portal, constructed with "piedra de Asperón" (Fig. 1), particularly crumbling and flaking, mainly in the lower section. The right half of the portal is better preserved than the left half, even though visually it looks worse due to a black crust. The decorative motifs in this half must be inferred from the ones preserved on the left half. The upper section of the portal is not as decayed, although there is some flaking of paint and crumbling in its lower part, which is linked to the entablature. The outer walls surrounding the façade are of travertine stone and are well preserved.

The "Asperon" stone, which predominates in the portal and shows the greatest amount of decay, was subjected to a mineralogical study including polarised light microscopy (Zeiss Jenapol model) and X-ray diffraction (XRD, PHILIPS PW 1710 diffractometer equipped with an automatic slit, University of Granada). Crystal powder analysis was also carried out with CuKa, 40 Kv, 40mA, 0.1 20/sec. The recording was made using computer programs (Martín-Ramos, 1990).

The texture of the samples was studied with a Jeol JSM 5800 scanning electron microscope (SEM) coupled to an Oxford ISIS 486 microanalyser from the University of Jaén and a Zeiss DMS 950 with a Microanalysis Link QX 2000 from the University of Granada.

Physical tests were undertaken with quarry material cut into 5 cm sided cubes. The behaviour of untreated samples (blank) and samples treated with consolidating and/or waterproofing products (Table 1) was compared with phenomena related to the movement of water inside the stone. The amount of water retained and/or displaced was determined, as well as the speed of this process in free absorption, desorption and capillarity tests, following several different norms (NORMAL 7/81; NORMAL 11/85; NORMAL 29/88). Based on the above values, we have calculated the open porosity, the ratio of pores and the true density.

Table 1. Treatments used.

Product	Kind	Concentration (%)	Composition
TEGOSIVIN HL 100 (T)	Protective	10	Modified siloxane without solvent
TEGOVAKON V (TK)	Consolidant	25	Organic compound of silicic ester and metilsiloxane
RHODORSIL RC 70 (R)	Consolidant	-	Catalysed tetraetoxilane (silicate of catalysed ethyl)
PARALOID B-72 (P)	Consolidant	5	Co-polymer of ethylmethacrylate
ESTEL 1000 (S)	Consolidant	-	Ethylic esthers of silicic acid (Si(OEt)4)n
ESTEL 1100 (ST)	Consolidant and protective	-	Ethylic esthers of silicic acid and oligomeric polisiloxanes

Among the techniques for determining physical properties, ultrasound procedures stand out due to their non-destructive nature. Therefore, the measurement of parameters related with the propagation of ultrasound waves through building materials (i.e., the velocity of longitudinal waves -Vp-, frequency, wave energy, etc.) comprises one of the best methods for physical characterisation. For this study we have used direct transmission with a STEINKAMP BP-5 apparatus, with 100 kHz frequency transductors for more precision in the measurements. Twenty measurements were made in each direction (referring to an orthogonal system) on three samples for each group with the same treatment. The values calculated correspond to: Vp1 (velocity of longitudinal waves perpendicular to the direction of sedimentation, in m/s); Vp2 and Vp3 (velocity parallel to the plane of sedimentation or to the direction of compaction, in m/s); structural anisotropy values, (M (total anisotropy in %) and (m (relative anisotropy in %) (Guydader and Denis, 1986), where:



This technique also allows the determination of the presence of possible anisotropies, the deduction of the state of the internal porosity/fissuring, the detection of different degrees of decay, and the evaluation of the variation undergone by the sample with the application of the consolidation and protection treatments, as well as the damage caused by the accelerated aging tests. We also carried out mechanical tests (compression strength) to determine the consolidating power of each treatment, correlating these data with the results of the ultrasound measurements.

In the accelerated aging tests the samples (treated and untreated) were subjected to salt crystallisation, freeze-thaw, and wet-dry cycles. The number of cycles depends on the durability of the sample and the aggressiveness of the test, repeating it until a high degree of decay or the total destruction of the samples is attained. The RILEM 25 PEM norm (1980) was followed. The damage produced by the accelerated aging tests was evaluated by visual inspection of the loss of material (the edges and corners of the samples were previously bevelled), as well as possible changes in colour, weight and in the Vp.

Results

Fig 2: X-ray diffractograms of Facade fragments (C3, C4, C5, C6) and quarry stones (Q14) (Ca=calcite; Q=quartz; Dol=dolomite.

The stone of the Lonja Portal ("Asperon" stone) has been classified as a calcarenite based on a study of its mineralogical composition with XRD (Fig. 2) and a petrographic study with light microscopy. According to Folk's classification (1962), it is a bioclastic calcarenite due to its micritic calcareous matrix and structure of grains comprising quartz, calcite, dolomite, scarce feldspar, and bioclast fragments, primarily equinoderms, bivalves, ostracods, and planktonic foraminifers. In addition, in accordance with Dunham (1962) and based on the original texture of the carbonate sediment, it can be termed a packestone.

The samples from the monument and from the quarry have evident textural differences. The building samples show greater porosity and fissuring, while the quarry samples are healthier-looking in both texture and structure. In some cases the church samples show secondary gypsum crystallisation in the cracks. Table 2 shows the results of the semi-quantitative analysis of the church and quarry samples.

Table 2. XRD mineralogical composition (in %) of church façade (C) and quarry (Q) samples.

	Quartz	Feldspar	Calcite	Dolomite	Gypsum
C1	19	-	36	-	45
C2	18	-	34	-	48
C3	15	-	59	26	-
C4	10	-	61	29	-
C5	17	-	58 2	5	-
C6	27	-	60	13	-
C7	10	16	63	11	-

Fig 3: General aspect of the C3 biocalcarenite.

Fig 4: Detail of C5 sample.

The SEM analyses of the most decayed samples from the portal were crucial in determining the causes of the deterioration. As can be seen in Figures 3 and 4, samples C3 and C6 are extremely porous, with small, uniform crystals. They are characterised by the presence, in addition to calcite, of phyllosilicates and various soluble salts. The latter two groups of minerals may be responsible for the intensive decay observed in the façade. The phyllosilicates are illite and smectites. The latter are capable of capturing water, increasing its volume by swelling, and then losing it with the same ease by shrinking, which can give rise to considerable internal pressures that fissure the stone. In addition to gypsum, we have also detected the presence of a complex salt with chloride and sulphate anions, more or less rounded. These minerals are hygroscopics, capable of capturing water and changing their size and crystalline phase depending on the temperature and relative humidity. Upon crystallising and/or hydrating inside the pores, they can create stresses that eventually produce crumbling and disaggregation of the stone in the church (Goudie and Viles, 1997).

The quarry samples were immersed for 10 minutes in one of the different products in Table 1, with no changes in their external appearance (colour, shine, etc.). The results of the tests compare data from untreated samples (i.e., blanks (B)) with treated samples.

Fig 5: Weight variations (DP) of samples after the first and the second treatment application versus time (T)

In all cases there is an increase in weight with the application of the treatments. After the application, the solvent begins to be lost, which is reflected in the drop in the curves at 15 days (Fig. 5). The drying is complete around the 4th week, when the weights stabilise.

The penetration of the treatments and the increase in weight of the samples depend on the type of treatment given. As may be seen in Figure 5, the greatest increases in weight occur with the application of: Estel 1000, Estel 1100, and Tegovakon V + Tegosivin HL 100 (the values are over 5% by weight), which means that higher amounts of these products are absorbed. The loss of solvent that begins from the 3rd week on is greatest for Tegovakon V + Tegosivin HL 100. The compound that penetrates the least is Paraloid B-72, at about 1% by weight, followed by Tegovakon V. In these two cases there is no loss of weight over time, indicating that the weight gain with the treatment is due to the reactive and not to the solvent. In the case of Rhodorsil RC-70 (a weakly protective consolidant), the behaviour is similar to Tegosivin HL 100 (protective), but in the latter there is a greater weight loss.

Table 3 presents the hydric behaviour of the treated samples. There is a decrease in porosity (calculated after saturation in a vacuum, that is, maximum saturation) in all of the treated samples. The greatest loss of porosity is observed in samples treated with Rhodorsil RC 70 (22.56%), Estel 1000 (23.56%), and Estel 1100 (23.71%). The density, both real and apparent, shows the same trend.

Table 3. Hydric parameters (P = open porosity; Ip = index of porosity; r _a = apparent density; r _r = real density; A = free absorption; S = saturation coefficient; C = capillarity).

	P (%)	Ip	r a	r r	A (%)	S (%)	C (%)
B	31.01	0.45	1.85	2.67	12.23	22.25	21.00
ST	23.71	0.31	1.95	2.55	12.14	23.70	1.63
S	23.56	0.31	1.95	2.56	12.05	23.57	1.89
P	28.86	0.40	1.88	2.65	15.30	28.87	13.22
R	22.56	0.29	2.01	2.59	11.23	22.56	4.34
TK	29.17	0.41	1.88	2.65	15.51	29.99	1.13
T	25.74	0.35	1.93	2.60	2.17	32.82	1.52
TK + T	24.39	0.32	1.93	2.55	12.65	24.39	0.99

Ip = 100/(100-P)

It is worth noting the high water content due to absorption in the samples treated with Paraloid B 72 and Tegovakon V. In contrast, the samples treated with Tegosivin HL 100, which absorb almost no water, have a greater amount of water from forced saturation. The untreated samples and those treated with Paraloid B-72 absorb the greatest amount of water and in the shortest time, suggesting that Paraloid B-72 has few water-repellent properties.

Fig 6: Water apsorption and water loss performance of treated samples.

Overall, as can be seen in Figure 6, there are two well-defined behaviours: a) similar to the blank samples in the case of stones treated with Paraloid B-72 (consolidating and weakly water repellent) or with Tegovakon V (consolidating), and b) the rest of the samples, with a low rate of free absorption of water (with the exception of Rhodorsil RC 70, which undergoes an abrupt increase after 36 hours). The samples least affected by vacuum saturation were those treated with Rhodorsil RC-70 (with a slightly lower value), in spite of it being weakly water repellent.

In the free desorption of water (drying), all the treated samples show curves very similar to the blank (Fig. 6). At the end of the test all the treated samples presented a weight loss of under 2%, with the exception of the samples treated with Paraloid B-72, thereby suggesting a partial loss of treatment after prolonged periods of immersion.

The highest values of capillary suction correspond to the blank and to the Paraloid B-72. The rest of the samples have a low rate of capillarity, indicating good behaviour with respect to water (Table 3).

Fig 7: SEM photomicrograph showing Tegovakon V failure to penetrate within the stone pores.

Fig 8: Salt efflorescence on a biocalcarenite treated with Tegovakon V after 10 salt crystallisation cycles.

Fig 9: Sample weight loss following salt crystallisation test.

SEM analysis shows the distribution and depth to which the treatments penetrate, revealing whether they remain near the surface or reach the inside of the material, consolidating at depth (Fig. 7). With the sole exception of Tegovakon V, all the products penetrate to the heart of the samples. SEM is also of use in evaluating the deterioration generated as the number of cycles of the accelerated aging tests increase (Fig. 8).

Ten cycles of salt crystallisation were carried out, producing in the blank an effect similar to that observed in the bases of the columns of the Lonja Portal. The results were satisfactory for most of the treatments (Fig. 9), with the exception of samples treated with Tegovakon V, where there is first a slight increase in weight in the first cycles followed by an abrupt fall at the end of the test. The total loss is more than 12% by weight due to progressive deterioration, with the loss of edges and the crumbling of the faces of the samples, a similar behaviour to that seen in the blank. Although this test is usually limited to 10 cycles, we increased it to 20, observing that, after 15 cycles, the stones treated with Estel 1000 and Estel 1100 began to deteriorate superficially on the faces, although the edges remained perfectly conserved. In the case of the Estel 1000 treated samples, breakage occurred along bedding planes.

The weight variation in the freeze-thaw and wet-dry tests is much less marked that in the salt cycles. There is a similar tendency in all cases, with a slight weight loss (around 1%-1.5% at most) that can be put down to the weighing method. Since the blank underwent no marked changes either, it would seem that cyclic changes in humidity, without taking into account the synergy of other factors associated with water, is not a factor directly responsible for decay in this type of stone.

At various stages of the accelerated aging tests we carried out ultrasound measurements to detect by NDT the development and intensity of damages that might escape visual inspection. When the data obtained here for the "Asperón" stone are compared with data on other ornamental stones widely used in Spanish Architectural Heritage, no substantial differences can be seen. It should be noted, however, that the ultrasound velocity propagation (3004 m/s) is medium-high when compared with a sandstone such as Salamanca (Martín-Patino et al., 1996). This is in contrast with its values of open porosity (31.01%), which are quite high in relation to stones such as the calcarenites of S. Pudia (Rodríguez-Navarro, 1998) and of Baeza (Sebastián-Pardo et al., 1995) or to the Piedramuelle limestone (Esbert et al., 1991). The components of the "Asperón" stone must therefore be strongly cemented.

The data for the "Asperón" stone (blank, Table 4) indicate it is quite homogeneous, with a low total ((M) and relative ((m) elastic anisotropy. The treatments that increase the ultrasound velocity the most, and therefore its compactability, are Estel 1100, Estel 1000 and Rhodorsil RC 70.

Table 4. Vp Values for "blank and treated samples.

	V1	V2	V3	D M	D m
B	3000	3009	3002	0.20	0.23
ST	3217	3317	3416	4.50	2.95
S	3248	3291	3219	0.30	2.20
R	3279	3244	3336	0.40	2.80
P	3142	3191	3182	1.50	0.27
TK	3028	3174	3102	3.50	2.88
T	3102	3163	3082	0.70	2.59
TK+T	3133	3158	3209	1.60	1.60

The ultrasound values are notably affected by the salt crystallisation tests. Table 5 illustrates the behaviour of the samples after the treatments, at 5 and 10 cycles. There is a systematic increase in Vp upon applying the treatments. At 5 cycles there is a decrease in Vp as the samples begin to develop fissures and the porosity increases in some samples with no observable fissuring. This behaviour may be due in part to the action of the salts on the treatment products (their destruction or loss). Once the topmost, or protective, layer of the treatment has been destroyed (at 10 cycles), the salts can penetrate the porous system more easily, filling it, which is reflected by an increase in the Vp. Only the samples treated with Tegovakon V + Tegosivin HL 100 show no variation in the Vp throughout the cycles.

Table 5. Vp values for "blank" and treated samples after 5 (a) and 10 (b) salt crystallisation cycles.

	V1a	V1b	V2a	V2b	V3a	V3b	D Ma	D Mb	D ma	D mb
B	2776	2904	2914	3248	2873	3040	4.07	7.63	1.44	6.61
ST	3099	3156	3110	3263	3158	3332	1.11	4.30	1.52	2.08
S	3055	3111	3111	3319	3182	3372	2.88	7.01	2.26	1.60
P	2952	3022	3035	3102	3035	3112	2.74	2.86	0.01	0.04
R	2994	3034	2916	3003	3054	3071	0.30	0.10	4.61	2.21
TK	2784	2812	2727	2817	2646	2811	3.62	0.09	3.03	0.19
T	2914	2938	2958	2996	3003	3087	2.23	3.41	1.53	2.97
TK+T	3152	3160	3285	3161	3229	3372	1.69	3.27	1.36	6.46

The anisotropy shows some changes between the distinct treatments, but never over 7%. If we take the blank and the sample treated with Tegovakon V (the two with the poorest results in this test), it can be seen how the anisotropy increases concomitantly with the number of salt crystallisation cycles.

The wet-dry test (Table 6) produces a slight decrease in the Vp of the samples as the total anisotropy increases, but the change is not as marked as in the salt test. The freeze-thaw test (Table 7) also causes a slight decrease in the velocities of the ultrasound waves.

Table 6. Vp values for "blank" and treated samples after 30 wetting-drying cycles.

	V1	V2	V3	D M	D m
B	2650	2950	2751	7.01	6.98
ST	3076	3020	3235	1.60	6.74
S	2912	2909	2971	0.93	2.10
P	3016	3125	3043	2.21	2.67
R	3091	3104	3112	0.56	0.26
TK	2743	2864	2781	2.79	2.74
T	3176	3121	3215	0.26	2.97
TK+T	3042	3173	3096	2.95	2.46

Table 7. Vp values for "blank" and treated samples after 15 freeze-thaw cycles.

	V1	V2	V3	D M	D m
B	2681	2651	2854	2.62	7.38
ST	3250	3162	3307	0.46	4.47
S	3193	3088	3197	1.59	3.48
P	2968	3038	3039	2.31	0.01
R	3034	2971	3086	0.05	3.80
TK	2852	2789	2913	0.03	4.35
T	2724	2777	2860	3.36	2.93
TK+T	3009	2876	3001	2.41	4.24

In both tests it is worth noting the better values (higher ultrasound wave propagation velocities) of the treated samples when compared with the blank. Plainly, any of the products increase the resistance to decay with respect to these particular weathering factors, since they provide the material with greater cohesion. Nonetheless, it is possible to rank the results from better to worse, that is, from greater to lesser Vp (greater to lesser cohesion and compactability): Estel 1100 > Rhodorsil RC 70 > Estel 1000 >> Tegovakon V + Tegosivin HL 100 >= Paraloid B-72 = Tegosivin HL 100.

The untreated and the treated samples were subjected to uniaxial compression tests. The lowest resistance is clearly the blank (145.77 kg/cm2) and, among the treated samples, Tegosivin HL 100 (which has no consolidating features (152.04 kg/cm2). The highest values correspond to Rhodorsil RC 70 (298.68 kg/cm2), Estel 1100 (312.37 kg/cm2), and Estel 100 (315.49 kg/cm2). Paraloid B-72 (155.19 kg/cm2), Tegovakon V (160.35 kg/cm2) and Tegovakon V + Tegosivin HL 100 (171.52 kg/cm2) have intermediate values. When these results are compared with the Vp values, there is an evident correspondence, with the lowest ultrasound propagation velocity being those of the blank and the samples treated with Tegosivin HL 100, while the highest values are those of the samples treated with Estel 1100, Rhodorsil RC 70 and Estel 1000.

Conclusions

The experimental results allow us to draw the following conclusions:

a) The optical microscope, SEM and XRD analyses show this rock (Piedra de Asperón) to be a porous calcarenite. This stone is quite durable and, therefore, suitable for building purposes. However, under extreme weathering conditions (e.g., wetting-drying, freeze-thaw, and salt crystallisation cycles) granular disintegration, crumbling and fissuring are observed in the lab. The very same weathering forms are observed to develop (at very low speed, if compared with the lab tests) in the building studied.

b) The main weathering mechanism in the building seems to be connected with water flow within the stone pores, where salt crystallisation and frost shattering may occur eventually. To a lesser extent, clay swelling/shrinking processes may also contribute to the stone decay. This is corroborated by accelerated aging tests.

c) A comparison of the water behaviour of blank (fresh quarry stone) and treated stone blocks allows the treatments to be ranked as follows (from best to worst): Estel 1100 ( Estel 1000 ( Tegosivin Hl 100 + Tegovakon V ( Tegosivin HL 100 > Rhodorsil RC 70 >> Tegovakon V ( Paraloid B-72 ( blank. The best treatment is considered the one that reduces water uptake and does not slow the drying process. All the products show a decrease in water-repellency after long-term storage under water (especially Paraloid B-72). This should be considered when designing a campaign for building treatment, since the studied church is placed in a high humidity environment (frequent rain, capillary rise and condensation).

d) Ultrasound speed (Vp) measurements show the calcarenite to be a compact, sound stone when fresh, with significant Vp reduction upon aging.

e) Salt crystallisation tests reveal significant differences among the various products tested, ranked (from best to worst) as follows: Tegovakon V + Tegosivin HL 100 > Estel 1100 ( Tegosivin HL 100 ( Rhodorsil RC 70 ( Estel 1000 >> blank > Tegovakon V > Paraloid B-72. This is corroborated by Vp and weight loss evolution and mechanical (compression strength) tests. In fact, throughout the whole set of analyses and tests, a good agreement is observed among Vp, water behaviour and compression test results.

f) Similar results as in the previous weathering test were obtained following wet/dry and freeze/thaw cycles.

We conclude that ultrasound speed (Vp) measurements are a non-destructive, efficient and accurate tool to evaluate the effectiveness of treatments in the lab, therefore being recommended for in-situ, on the building, treatment evaluation.

Acknowledgements

This study was financially supported by the Research Group RNM-0179 of the Junta de Andalucía and by the Research Project PB 96-1445 (DGICYT) and Consejería de Cultura of Granada. We are grateful to Christine Laurin for her assistance in translating the original text.

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