glass: Glass composition data

In ordr: A 'Tidyverse' Extension for Ordinations and Biplots

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. \Sexpr[results=rd]{tools:::Rd_expr_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)

ordr documentation built on Aug. 8, 2025, 7:27 p.m.