Smartphone photos as a non-destructive approach to characterise siliceous artefacts

Figures & data

Figure 1. Localisation of La Calvera rock-shelter in the Iberian Peninsula.

Figure 2. Picture of example sampled rocks: raw material chunk of dark grey chert (a: RM01), dark grey chert flakes (b: AR11; c: AR21), whitish chert (d: AR23), yellowish chert (e: AR38.2), quartzite (f: AR27), rock crystal (g: AR20) and Domeño chert fragment (h: AN01.2).

Figure 3. Flowchart for image analysis.

Table 1. Average values and standard deviations of CIELAB colour space parameters obtained by imaging of smartphone photos.

Sample	Class	L*			a*			b*			Sample	Class	L*			a*			b*
RM01	RM	34.7	±	8.5	2.3	±	1.0	−6.4	±	2.7	AR18.2	GC	44.3	±	7.4	3.2	±	1.2	−5.2	±	1.8
RM02	RM	36.4	±	7.7	2.1	±	0.9	−6.4	±	3.0	AR18.3	GC	46.8	±	7.7	4.1	±	1.6	−3.1	±	1.2
RM03.1	RM	31.5	±	5.6	2.2	±	0.7	−8.8	±	1.6	AR18.4	GC	40.8	±	11.6	4.1	±	1.9	−6.6	±	2.8
RM03.2	RM	42.9	±	8.2	2.9	±	1.3	−6.6	±	1.9	AR19	GC	43.3	±	9.3	2.7	±	1.2	−7.5	±	2.3
RM03.3	RM	38.7	±	6.9	2.8	±	0.9	−7.4	±	1.8	AR21	GC*	67.1	±	8.2	5.1	±	1.7	10.0	±	2.6
RM03.4	RM	38.3	±	6.4	2.2	±	0.9	−5.9	±	1.6	AR23	WC	91.7	±	2.7	0.6	±	0.5	11.3	±	1.2
RM03.5	RM	39.8	±	8.4	1.7	±	1.0	−4.9	±	1.7	AR24	QZ	66.7	±	16.2	3.2	±	1.5	9.1	±	3.8
RM03.6	RM	37.8	±	8.8	2.3	±	1.1	−6.0	±	1.7	AR26	QZ	52.2	±	11.0	7.1	±	2.3	13.7	±	3.9
RM04	RM	37.6	±	11.3	3.0	±	1.3	−4.6	±	3.1	AR27	QZ	43.1	±	11.1	4.5	±	1.5	5.4	±	2.3
RM05	RM	41.5	±	11.2	2.3	±	1.3	−3.1	±	3.1	AR28	QZ	38.6	±	13.6	4.3	±	1.4	1.7	±	2.9
AR01	GC	40.0	±	10.8	3.9	±	1.3	−8.0	±	2.2	AR29	QZ	51.9	±	14.6	6.2	±	2.0	7.3	±	3.0
AR02	GC	35.2	±	11.5	3.5	±	1.4	−9.0	±	2.7	AR30	QZ	49.8	±	9.7	4.7	±	1.2	4.8	±	1.5
AR03	GC	34.7	±	9.9	3.6	±	1.4	−8.9	±	2.7	AR31	QZ	50.4	±	13.2	5.4	±	2.4	6.8	±	4.2
AR04	GC	35.8	±	13.1	3.3	±	1.5	−8.6	±	3.7	AR32	QZ	62.2	±	9.7	6.5	±	2.7	8.4	±	2.7
AR06	GC	30.4	±	10.2	4.2	±	1.4	−9.8	±	2.7	AR33	QZ	43.1	±	11.5	4.6	±	2.0	7.5	±	5.7
AR07	GC	43.8	±	8.2	3.7	±	1.4	−5.6	±	1.9	AR34	QZ	46.8	±	13.4	5.7	±	1.6	5.3	±	3.9
AR08	QZ	47.0	±	12.3	1.1	±	1.5	−2.6	±	2.8	AR35	QZ	45.7	±	12.3	4.5	±	1.7	6.1	±	3.2
AR09	WC	87.9	±	3.1	−1.0	±	0.7	8.0	±	0.8	AR36.1	QZ	55.2	±	11.7	5.3	±	1.9	9.8	±	2.5
AR11	GC	36.3	±	8.8	3.6	±	1.4	−6.8	±	2.5	AR36.2	QZ	60.1	±	10.3	5.4	±	1.7	8.7	±	2.4
AR12.1	GC	39.5	±	8.8	3.2	±	1.3	−7.0	±	1.8	AR36.3	QZ	48.0	±	10.6	7.3	±	1.7	7.8	±	2.5
AR12.2	GC	38.7	±	9.8	3.3	±	1.3	−6.2	±	2.1	AR37	YC	73.0	±	9.1	5.5	±	3.9	33.4	±	9.5
AR12.3	GC	37.1	±	7.9	3.3	±	1.3	−7.2	±	1.7	AR38.1	YC	72.9	±	9.4	7.8	±	5.0	27.3	±	7.3
AR12.4	GC	31.3	±	11.6	3.9	±	1.4	−9.4	±	3.3	AR38.2	YC	79.5	±	6.1	3.7	±	2.4	29.0	±	11.9
AR12.5	GC	36.7	±	13.4	4.4	±	1.7	−5.1	±	4.7	AN01.1	DC	37.6	±	11.7	4.5	±	1.4	0.0	±	1.6
AR12.6	GC	40.3	±	11.5	3.5	±	1.4	−7.4	±	3.0	AN01.2	DC	42.9	±	9.5	4.0	±	1.1	1.6	±	1.4
AR12.7	GC	46.6	±	12.9	4.1	±	1.6	−4.8	±	4.2	AN01.3	DC	39.1	±	9.9	4.1	±	1.0	0.6	±	1.2
AR13.1	GC	38.9	±	10.7	3.6	±	1.4	−7.8	±	2.4	AN02.1	DC	57.4	±	7.6	3.9	±	0.9	6.5	±	1.2
AR13.2	GC	36.7	±	11.0	3.5	±	1.5	−7.1	±	2.9	AN02.2	DC	64.2	±	5.8	3.2	±	1.1	7.1	±	1.0
AR13.3	GC	42.2	±	9.3	3.6	±	1.4	−5.9	±	2.0	AN02.3	DC	55.4	±	4.2	5.2	±	0.9	9.3	±	0.7
AR14	GC	37.3	±	10.8	3.7	±	1.5	−8.0	±	2.3	AN04.1	DC	48.1	±	9.4	4.4	±	1.0	6.3	±	1.3
AR15	GC	47.0	±	7.2	2.7	±	1.1	−5.4	±	1.7	AN04.2	DC	47.6	±	11.5	3.9	±	1.1	5.5	±	1.8
AR16	GC	46.4	±	9.8	3.2	±	1.3	−4.1	±	2.5	AN04.3	DC	45.3	±	8.5	4.3	±	1.1	5.1	±	1.1
AR17.1	GC	36.4	±	9.8	2.8	±	1.2	−6.7	±	2.5	AN05.1	DC	46.6	±	9.9	4.5	±	1.0	4.3	±	1.5
AR17.2	GC	34.1	±	9.8	3.4	±	1.5	−8.1	±	2.7	AN05.2	DC	53.0	±	5.0	4.2	±	0.6	5.9	±	0.8

Note: RM = chunks of raw material; GC = grey chert; GC* = other grey chert; WC = white chert, DC = Domeño chert; YC = yellow chert; QZ = quartzite.

Table 2. Average values and standard deviations of CIELAB colour space parameters obtained by Vis-SP.

Sample	Class	L*			a*			b*			Sample	Class	L*			a*			b*
RM01	RM	29.7	±	3.8	0.2	±	0.3	1.4	±	2.1	AR17.2	GC	28.0	±	1.6	0.1	±	<0.1	0.5	±	0.4
RM02	RM	28.8	±	2.5	0.1	±	<0.1	1.1	±	0.8	AR18.2	GC	28.7	±	1.3	0.2	±	0.1	1.0	±	0.4
RM03.1	RM	28.5	±	3.6	0.2	±	0.1	0.8	±	1.2	AR19	GC	31.0	±	2.0	−0.2	±	<0.1	0.6	±	0.4
RM03.2	RM	27.3	±	0.5	0.1	±	<0.1	0.5	±	0.4	AR21	GC*	48.8	±	0.8	1.5	±	<0.1	7.4	±	0.1
RM03.3	RM	29.7	±	1.5	0.1	±	<0.1	0.4	±	0.2	AR23	WC	83.1	±	0.3	1.9	±	0.1	13.8	±	0.9
RM03.4	RM	28.6	±	0.8	0.3	±	0.2	1.1	±	0.3	AR24	QZ	41.3	±	8.6	0.5	±	0.6	4.0	±	2.2
RM03.5	RM	30.2	±	4.5	0.0	±	0.1	1.1	±	0.8	AR26	QZ	39.3	±	0.3	1.5	±	0.4	6.9	±	0.8
RM03.6	RM	29.8	±	1.2	0.2	±	0.1	1.0	±	0.5	AR27	QZ	36.7	±	2.4	0.7	±	0.2	5.5	±	0.9
RM04	RM	29.8	±	1.5	0.6	±	0.1	1.5	±	0.4	AR28	QZ	33.6	±	0.9	0.3	±	0.1	2.4	±	0.7
RM05	RM	28.9	±	2.7	0.4	±	0.2	0.9	±	1.1	AR29	QZ	40.2	±	3.5	1.8	±	0.8	5.6	±	1.3
AR01	GC	27.9	±	0.6	0.3	±	<0.1	1.0	±	0.4	AR30	QZ	43.0	±	1.3	0.8	±	0.3	5.7	±	1.2
AR02	GC	27.1	±	0.8	0.3	±	0.1	0.4	±	0.3	AR31	QZ	38.2	±	1.5	1.2	±	0.6	5.5	±	1.5
AR03	GC	28.4	±	1.4	0.1	±	<0.1	0.7	±	0.7	AR32	QZ	48.9	±	4.3	1.8	±	0.4	6.6	±	1.2
AR04	GC	27.1	±	2.1	0.3	±	0.3	1.2	±	1.3	AR33	QZ	41.0	±	5.7	2.7	±	3.6	8.3	±	6.6
AR06	GC	25.8	±	0.4	0.2	±	<0.1	0.5	±	0.1	AR34	QZ	39.1	±	1.9	1.3	±	0.1	5.3	±	1.0
AR07	GC	33.2	±	0.4	0.1	±	<0.1	1.1	±	0.1	AR35	QZ	34.4	±	2.2	0.5	±	0.4	4.4	±	1.2
AR08	QZ	33.9	±	2.7	−1.0	±	0.2	2.8	±	0.9	AR36.1	QZ	50.9	±	1.3	1.2	±	0.3	6.0	±	1.0
AR09	WC	75.0	±	1.0	−0.1	±	0.5	9.1	±	2.2	AR36.2	QZ	39.8	±	2.2	1.8	±	<0.1	7.7	±	0.4
AR11	GC	28.2	±	0.4	0.4	±	0.1	1.4	±	0.1	AR36.3	QZ	39.2	±	1.0	2.3	±	0.2	5.5	±	0.4
AR12.1	GC	30.4	±	4.2	0.3	±	0.1	1.5	±	0.5	AR37	YC	56.6	±	5.3	8.3	±	2.2	25.4	±	2.1
AR12.2	GC	29.0	±	1.5	0.1	±	0.1	1.9	±	0.4	AR38.2	YC	45.6	±	2.3	7.9	±	1.8	17.3	±	2.8
AR12.3	GC	30.6	±	2.6	0.5	±	0.2	1.6	±	0.4	AN01.1	DC	34.6	±	0.1	0.9	±	<0.1	3.7	±	0.1
AR12.4	GC	27.7	±	0.7	0.1	±	<0.1	0.3	±	0.2	AN01.2	DC	34.2	±	0.8	0.5	±	<0.1	2.3	±	0.3
AR12.5	GC	28.7	±	0.3	0.2	±	0.1	0.8	±	<0.1	AN01.3	DC	36.3	±	0.2	0.7	±	0.1	3.2	±	0.4
AR12.6	GC	30.3	±	0.8	0.2	±	0.5	1.1	±	1.6	AN02.1	DC	49.0	±	1.2	1.5	±	0.3	6.8	±	0.8
AR13.1	GC	27.3	±	0.3	0.2	±	0.1	0.7	±	0.1	AN02.2	DC	54.9	±	0.4	1.5	±	0.1	7.4	±	0.2
AR13.2	GC	27.9	±	0.2	0.2	±	<0.1	0.7	±	<0.1	AN02.3	DC	45.6	±	1.7	2.3	±	0.3	8.4	±	0.6
AR13.3	GC	35.8	±	1.4	0.8	±	0.1	6.0	±	0.9	AN04.1	DC	42.7	±	1.9	1.4	±	0.1	5.9	±	0.7
AR14	GC	31.6	±	0.4	0.3	±	0.1	−0.2	±	0.2	AN04.2	DC	39.4	±	1.4	1.5	±	0.2	5.6	±	0.3
AR15	GC	33.0	±	0.4	0.1	±	0.5	1.3	±	1.4	AN04.3	DC	40.1	±	4.7	1.5	±	0.1	6.4	±	0.7
AR16	GC	29.5	±	0.5	0.2	±	0.1	1.3	±	0.4	AN05.1	DC	44.0	±	2.9	1.5	±	<0.1	6.4	±	0.3
AR17.1	GC	29.7	±	2.2	0.0	±	0.1	2.2	±	1.6	AN05.2	DC	47.1	±	3.8	1.7	±	0.1	6.7	±	0.5

Note: RM = chunks of raw material; GC = grey chert; GC* = other grey chert; WC = white chert, DC = Domeño chert; YC = yellow chert; QZ = quartzite.

Figure 4. Results of colour analysis: (a) Heatmap of L*, a* and b* for AR03 (see Table 1 for mean, µ, and standard deviation, σ); (b) comparison between colour analysis carried out by Vis-SP and imaging; (c) scatter plot for L* vs b* obtained by imaging of smartphone pictures.

Figure 5. DRIFT (a) and Raman (b and c) spectra for the different types of samples. Spectra were scaled by standard normal variate (SNV) and they are offset to avoid overlapping.

Figure 6. Samples/scores plot (a) and variables/loadings plots for PC1 (b) and PC2 (c).

Figure 7. Cluster analysis of smartphone imaging (a) and pXRF (b) results.