glass {ordr}

Glass composition data

Description

Sites, types, and compositions of glass samples from archaeological sites in Israel.

Usage

data(glass)

Format

A tibble with 68 cases and 16 variables:

Site

site at which sample was found

Anal

analysis identifier

Context

furnace identifier

Form

type of sample

SiO2, TiO2, Al2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, Cl, SO3

normalized weight percent oxide of each component

Details

Chunks of unformed glass from several furnaces found at the primary Byzantine-era site of Bet Eli'ezer, along with samples from other sites with weaker evidence of glass-making (Apollonia and Dor) and and from an Islamic-era site (Banias), were analyzed using X-ray spectrometry to determine their major components.

Baxter & Freestone (2006) used these data to illustrate log-ratio analysis.

Source

Freestone &al (2000), Table 2.

References

Freestone IC, Gorin-Rosen Y, & Hughes MJ (2000) "Primary glass from Israel and the production of glass in Late Antiquity and the early Islamic period". La route du verre: Ateliers primaires et secondaires du second millénaire av. J.-C. au Moyen Âge: 65–83. https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=1158762

Baxter MJ & Freestone IC (2006) "Log-Ratio Compositional Data Analysis in Archaeometry". Archaeometry, 48(3): 511–531. doi:10.1111/j.1475-4754.2006.00270.x

Examples

# subset glass data to one site and major components
head(glass)
glass_main <- subset(
  glass,
  Site == "Bet Eli'ezer",
  select = c("SiO2", "Na2O", "CaO", "Al2O3", "MgO", "K2O")
)
# format as a data frame with row names
glass_main <- as.data.frame(glass_main)
rownames(glass_main) <- subset(glass, Site == "Bet Eli'ezer")$Anal

# perform log-ratio analysis
glass_lra <- lra(glass_main, compositional = TRUE, weighted = FALSE)
# inspect LRA row and column coordinates
head(glass_lra$row.coords)
glass_lra$column.coords
# inspect singular values of LRA
glass_lra$sv

# plot samples and measurements in a biplot
biplot(
  x = glass_lra$row.coords %*% diag(glass_lra$sv),
  y = glass_lra$column.coords,
  xlab = "Sample (principal coord.)", ylab = ""
)
mtext("Component (standard coord.)", side = 4L, line = 3L)