Glass Does Its Real Work by Dissolving

In 1969, a ceramic engineer named Larry Hench sat on a bus next to a U.S. Army colonel who had just come from Vietnam. The colonel asked whether science could build something to help bodies regenerate the bone and tissue being lost to war. Hench went back to his lab and mixed sodium, calcium, phosphorus, and silica into a glass — 45S5 Bioglass — that bonded to living bone, the first synthetic material ever to do so [1]. The mechanism was dissolution. When the glass contacted bodily fluids, its surface broke down and released ions that prompted osteoblasts to start growing new bone. The material worked because it disappeared. The FDA cleared the first Bioglass device, a middle ear prosthesis, in 1985 [2]. By the 1990s particulate Bioglass was in clinical use for periodontal bone repair, and the same chemistry now turns up in Sensodyne toothpaste sold outside the United States, where NovaMin releases ions that remineralize enamel [3].

Diatoms have been at this for roughly 180 million years. These single-celled algae build shells of nanostructured silica called frustules, using proteins called silaffins that precipitate glass at ambient temperature and pressure [4]. There are an estimated 100,000 diatom species, and they account for roughly 40% of marine primary production [5]. Collectively they pull about 6.7 billion metric tons of silicon from seawater each year [6]. When diatoms die, their shells sink. Some dissolve in the upper ocean, recycling silicon for the next generation; the rest reach the seafloor carrying organic carbon, part of a burial system that regulates atmospheric CO₂ [7]. The frustules that make it that far have the highest strength-to-weight ratio of any known biological material [8]. The whole system depends on dissolution rates. Diatom populations fell more than 1% per year globally from 1998 to 2012 [9], and ocean acidification is now slowing silica dissolution, which suppresses diatom growth in turn — a feedback loop with direct consequences for the carbon cycle [10].

Britain spent 155 years getting this backwards. The Window Tax, introduced in 1696, assessed property by counting windows — a proxy for wealth before income tax existed [11]. The Glass Tax, added in 1746, initially hit raw materials, then shifted to finished goods in 1811, eventually exceeding 300% of the glass’s value [12]. The Lancet called it an “absurd impost on light” in 1845, blaming the cost of glass for the dangerous darkness of urban housing [12]. The burden pushed manufacturers to Ireland, where a 1780 tax exemption helped establish Waterford Crystal in 1783 [13]. Both taxes were repealed by 1851.

The state treated glass as a fixed asset: countable, weighable, tariffable. But glass’s contribution to the world has almost nothing to do with its mass. A window matters because light passes through it. Bioglass matters because it disappears into new bone. Diatom shells matter because they dissolve fast enough to feed the next generation and slow enough to drag carbon into the deep. The British tax code never accounted for any of that. It saw solid, transparent stuff and slapped a duty on the poundage.

References

[1] National Academy of Engineering, “Larry L. Hench 1938–2015” — https://www.nae.edu/219802/LARRY-L-HENCH-19382015

[2] Hench, L.L., “The story of Bioglass,” J. Mater. Sci.: Mater. Med., 2006 — https://pubmed.ncbi.nlm.nih.gov/17122907/

[3] Haleon, “NovaMin Toothpaste Science” — https://www.haleonhealthpartner.com/en-gb/oral-health/brands/sensodyne/science/novamin/

[4] Sumper, M. & Brunner, E., “Silaffins,” Marine Drugs, 2015 — https://pmc.ncbi.nlm.nih.gov/articles/PMC4557024/

[5] Falciatore, A. & Bowler, C., “The evolution of diatoms,” Annu. Rev. Ecol. Evol. Syst., 2016 — https://pmc.ncbi.nlm.nih.gov/articles/PMC5516106/

[6] Round, F.E. et al., The Diatoms, 1990 — https://en.wikipedia.org/wiki/Diatom

[7] Trull, T.W. et al., “Sinking Diatom Assemblages,” Front. Earth Sci., 2021 — https://www.frontiersin.org/articles/10.3389/feart.2021.579198

[8] Aitken, Z.H. et al., Caltech, 2016 — https://www.caltech.edu/about/news/tiny-diatoms-boast-enormous-strength-49767

[9] NASA, “Dwindling Diatoms” — https://svs.gsfc.nasa.gov/11934

[10] Taucher, J. et al., “Slower silica dissolution under ocean acidification,” Nature, 2022 — https://doi.org/10.1038/s41586-022-04687-0

[11] “Window tax,” Wikipedia — https://en.wikipedia.org/wiki/Window_tax

[12] “Glass tax,” Wikipedia, citing The Lancet 1:214–215, 1845 — https://en.wikipedia.org/wiki/Glass_tax

[13] “Glass tax,” Wikipedia (1780 Irish exemption) — https://en.wikipedia.org/wiki/Glass_tax