Convert Rankine to Wedgwood easily.

If you’ve ever stumbled across an 18th-century pottery manual or a pre-Victorian engineering journal, you might’ve seen temperatures listed in "degrees Wedgwood." This obscure unit, alongside the more technical Rankine scale, tells a story of human ingenuity in an era before standardized measurement. Let’s unravel how these two scales intersect and why converting between them is like translating whispers from the Industrial Revolution.

Unit definitions

What is a Rankine (°R)?

The Rankine scale, named after Scottish engineer William Rankine, measures absolute temperature starting at zero (absolute zero). Each degree Rankine equals one degree Fahrenheit, making it familiar to Americans but with a thermodynamic twist. You’ll spot it in niche engineering contexts, like U.S. aerospace thermal calculations. Its symbol? A simple °R.

What is a Wedgwood (°W)?

Josiah Wedgwood, the English pottery magnate, invented this scale around 1782 to gauge kiln temperatures. Unlike Rankine, Wedgwood units (°W) weren’t based on air expansion or mercury. Instead, they tracked how much clay samples shrank when fired. One °W roughly equaled 130°F, but inconsistencies in clay composition made it unreliable. By the mid-1800s, it was obsolete.

Conversion formula

Since Wedgwood’s scale isn’t formally defined in modern terms, historians and scientists approximate the relationship:

°W = (°R - 459.67 - 32) / 130

Simplifying, we get:

°W ≈ (°R / 130) - 3.536

For reverse calculations:

°R ≈ (°W + 3.536) * 130

Remember, these formulas are best-guess estimates. Treat them like a faded map—useful but not GPS-accurate.

Example calculations

1. Converting 1000°R to Wedgwood:

   1000 / 130 - 3.536 ≈ 7.69 - 3.536 = 4.15°W
   

   
   A kiln at 1000°R would’ve been labeled ~4.15°W in Wedgwood’s day.
2. Converting 5°W to Rankine:

   (5 + 3.536) * 130 ≈ 8.536 * 130 = 1109.68°R
   

   
   Wedgwood’s 5°W equals roughly 1109.68°R—a searing heat for porcelain.

Conversion tables

Rankine to Wedgwood

Wedgwood to Rankine

Historical background

The Wedgwood scale emerged from pottery workshops, not laboratories. Josiah Wedgwood needed a way to replicate high-temperature glazes consistently. His solution? Fire small clay cylinders and measure their shrinkage. A 1/5th shrinkage became 1°W. While innovative, the system had flaws. Different clay batches shrank unpredictably, and the scale couldn’t benefit from precise thermocouples (invented centuries later). By contrast, Rankine’s 1859 scale built on Lord Kelvin’s work, anchoring temperature to molecular motion, a concept Wedgwood’s era couldn’t grasp.

Interesting facts

1. Pottery or Pyrometrics? Wedgwood’s kilns reached ~1100°C, yet his scale only went up to 27°W. That’s like measuring a marathon with a yardstick.
2. Fahrenheit’s Shadow: Rankine’s scale mirrored Fahrenheit’s increments, making it intuitive for steam engine engineers.
3. Clay Calculus: To measure shrinkage, Wedgwood used a "pyrometric bead" that deformed at specific temps—a primitive but effective indicator.
4. Thermodynamic Twins: Rankine and Kelvin scales both start at absolute zero, but Rankine stuck with Fahrenheit’s degree size.
5. A Scale Forgotten: By 1840, the Wedgwood unit vanished from textbooks, replaced by Daniell’s pyrometer and later, the thermocouple.

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