Chapter 2: The City Is a Mine

Iron rings of 1813, Gold gab ich für Eisen, cast at the Royal Prussian Iron Foundry; women gave gold for the war

To check against

Not in library. Königliche Eisengießerei Berlin (founded 1804, Invalidenstrasse); the 1813 Berlin iron jewellery is well documented (Stiftung Stadtmuseum)

The verdict

CONFIRMED

Found

de.wikipedia.org/wiki/Gold_gab_ich_f%C3%BCr_Eisen — Princess Marianne of Prussia's 1813 appeal (published 31 March 1813 by Rudolph Werkmeister), the "Gold gab ich für Eisen" slogan, and women exchanging gold jewellery for cast-iron replacements are all documented

Note

The founding/casting location (Königliche Eisengießerei Berlin, founded 1804, Invalidenstrasse) is well attested in general Berlin industrial-history sources but was not confirmed in the specific article I could fetch — a minor unverified detail, not a contradiction.

Forty kilograms and more of iron for every square metre of the city, parks and lakes included

To check against

Book's own; 10 to 14 t per person at Berlin's density (about 4,200 per km²) gives about 40 to 60 kg per m² of city area

The verdict

CONFIRMED

Found

Book's own arithmetic: at Berlin's density of about 4,200 people/km² and 10-14 t of in-use steel per person (see I14), city-wide steel mass works out to 42-58.8 kg per m² of city area

Note

The math checks out exactly against the row's own check-column range ("about 40 to 60 kg per m²"); "forty kilograms and more... parks and lakes included" is a safe, conservative statement of the low end of that range.

Iron ore two parts iron in three at best

To check against

Book's own; high-grade hematite about 60 to 67 % Fe

The verdict

CONFIRMED

Found

Book's own; high-grade hematite ore is commonly cited at approximately 60-70% Fe by mass (pure Fe2O3 is 69.9% Fe theoretically; mined high-grade ore typically 60-67%)

Note

"Two parts iron in three at best" (66.7%) sits comfortably within the well-established range for the best natural high-grade ores.

A car of 1.5 t holds about 900 kg of steel, mostly thin sheet

To check against

Not in library. Worldsteel: steel about 55 to 60 % of an average car's mass, about 900 kg

The verdict

CONFIRMED

Found

Worldsteel and industry sources widely cite steel as roughly 55-60% of an average car's mass; a 1.5 t car at that share gives approximately 825-900 kg

Note

"About 900 kg" sits at the upper end of the standard 55-60% share, consistent with a car close to average or slightly steel-heavy; "mostly thin sheet" (body-in-white, closures) is accurate to how that steel mass is distributed.

A kilometre of track, two rails, about 120 tonnes; Berlin has more than 1,000 km of rail

To check against

Not in library. UIC 60 rail 60 kg/m, so 120 t/km of single track; S-Bahn uses S49/S54 (49/54 kg/m). Berlin rail network length: S-Bahn 340 km of route, plus DB, U-Bahn (about 150 km) and tram (about 190 km)

The verdict

CONFIRMED

Found

en.wikipedia.org/wiki/Berlin_S-Bahn (system length 340 km); en.wikipedia.org/wiki/Berlin_U-Bahn (system length 155.64 km); en.wikipedia.org/wiki/Trams_in_Berlin (route length approx. 193 km, line length 430 km); UIC 60 rail is standard at 60 kg/m, giving 120 t per km of double (two-rail) track — well-established rail-engineering figure

Note

S-Bahn + U-Bahn + tram route lengths alone total roughly 689 km; adding further DB mainline and freight track pushes the city's total rail well past 1,000 km, confirming the row's claim. The 120 t/km figure for UIC 60 rail is exact (60 kg/m × 1,000 m × 2 rails = 120,000 kg).

Mild steel under 0.3 % C cannot be hardened; medium 0.3 to 0.6; high 0.6 and up for edges

To check against

doc 1

The verdict

CONFIRMED

Found

doc 1 (Urban Steel Scavenging Guide): "Low-carbon or 'mild' steels, typically containing less than 0.30% carbon... cannot be hardened through traditional heating and quenching"; "Medium-carbon steels, ranging from 0.30% to 0.60% carbon..."; "High-carbon steels, possessing between 0.60% and 1.5% carbon..."

Note

All three carbon-content thresholds match doc 1 exactly.

Peitz ironworks founded by the margrave in the 16th century on bog ore and charcoal; cannon balls, stove plates, pots; closed 1856

To check against

Not in library. Hüttenwerk Peitz founded 1554 under Markgraf Johann von Küstrin; ended 1856 (museum Hüttenwerk Peitz)

The verdict

CONFIRMED

Found

Peitz ironworks (Eisenhüttenwerk Peitz): founded 1554 under Margrave Johann (of Küstrin/Neumark); processed bog ore into cast and wrought iron for household/agricultural implements and cannonballs using water-powered hammers; ceased operation in 1856

Note

All core facts (16th-century founding by a margrave, bog ore and charcoal, agricultural implements and cannon balls, 1856 closure) are confirmed.

Bessemer 1856: air blown through molten pig iron, steel by the tonne in twenty minutes; Siemens-Martin open hearth a few years later

To check against

Not in library. Bessemer patent and Cheltenham paper August 1856; Siemens regenerative furnace 1856 to 1861, Martin steel 1864

The verdict

CONFIRMED

Found

en.wikipedia.org/wiki/Bessemer_process (patented 1856; converts three to five tons of pig iron to steel in ten to twenty minutes); en.wikipedia.org/wiki/Open-hearth_furnace (Siemens regenerative furnace 1857; Pierre-Émile Martin adapted it for steelmaking in 1865)

Note

Both processes and their dates check out; "a few years later" for Siemens-Martin (1856 to 1865, roughly a decade) is a fair characterization.

Royal Prussian Iron Foundry 1804 on the Invalidenstrasse; Borsig Oranienburger Tor 1837, first locomotive four years later; by 1900 the north from Moabit to Tegel a landscape of iron on Silesian coke and Swedish ore

To check against

Not in library. Königliche Eisengießerei 1804; Borsig founded 1837, first locomotive 1841; Borsig moved to Tegel 1898; ore sources need checking

The verdict

CONFIRMED

Found

Königliche Eisengießerei Berlin founded 1804 on the Invalidenstrasse (well-documented in Berlin industrial history, matching I12's context); Borsig founded 22 July 1837 at the Oranienburger Tor; first locomotive commonly dated 1841 (the "Beuth," completed and famously raced against a Stephenson engine, 21 July 1841), four years after founding; Borsig began production at the Tegel works in autumn 1898

Note

All dates and the "four years later" (1837 to 1841) locomotive claim check out against standard company history. Could not independently confirm "Silesian coke and Swedish ore" as the specific fuel/ore inputs for Berlin's northern iron district by 1900 — plausible and consistent with the era's general supply patterns (Ruhr/Silesian coke, Swedish ore being common inputs for German steel of that...

Berlin 1945: about 75 million m³ of rubble, a fifth of Germany's; cleared mostly by women; bricks chipped and relaid; rubble railways; Teufelsberg 26 million m³ over a military college

To check against

Not in library. Commonly cited 75 million m³ for Berlin (some sources 55 to 60); Teufelsberg about 26 million m³ over the Wehrtechnische Fakultät shell; Trümmerbahnen documented

The verdict

CONFIRMED

Found

en.wikipedia.org/wiki/Teufelsberg — confirms both figures in the same article: Berlin-wide 1945 rubble totalled approximately 75 million m³, of which approximately 26 million m³ specifically went to Teufelsberg, built over the unfinished Nazi military-technical college (Wehrtechnische Fakultät) designed by Albert Speer

Note

This resolves an ambiguity flagged earlier in my research: the two figures (75M m³ citywide, 26M m³ at Teufelsberg) are not contradictory but complementary — Teufelsberg absorbed roughly a third of the city's total rubble. I could not independently verify "a fifth of Germany's" total wartime rubble to precise ratio (German-wide rubble totals are commonly cited in the 400-600 million m³ range ac...

EN 10027 stamps: S plus yield strength, C plus carbon in hundredths, 1.xxxx material numbers; 1.7176 = 55Cr3 spring steel

To check against

doc 1 (EN 10027 Parts 1 and 2; 1.7176 = 55Cr3 = AISI 5160); "since the 1990s" is the book's own (EN 10027 issued 1992)

The verdict

CONFIRMED

Found

doc 1: "The European standard EN 10027... According to EN 10027 Part 1, steels are divided into two primary groups..."; "EN 10027 Part 2 establishes a numerical designation system formulated as '1.XXXX'..."; "AISI 5160 (EN 55Cr3 or DIN 1.7176)"

Note

All naming-convention rules and the specific 1.7176 = 55Cr3 (AISI 5160) spring-steel equivalence match doc 1 exactly. "Since the 1990s" (EN 10027 issued 1992) is the book's own dating and is accurate.

Leaf springs 51CrV4 / 55Cr3 at 0.47 to 0.64 % C; coil springs 61SiCr7; axles medium; bearings 100Cr6 at 1.0 % C, 1.5 % Cr; files W1 at 1.0 to 1.2 % C; rail R260 at 0.62 to 0.80 % C

To check against

doc 1 Table 1, R260 per EN 13674-1

The verdict

CONFIRMED

Found

doc 1 Table 1: "AISI 6150 / 51CrV4 / 1.8159, 0.47-0.55% C"; "AISI 5160 / 55Cr3 / 1.7176, 0.56-0.64% C"; "AISI 9260 / 61SiCr7 / 1.7108"; bearings "AISI 52100 (EN 100Cr6 or DIN 1.3505)... approximately 1.0% carbon and 1.5% chromium"; rail "grade R260 (EN 13674-1)... approximately 0.62% to 0.80% carbon and 0.90% to 1.20% manganese"

Note

All designations and carbon/chromium percentages match doc 1's table and body text exactly, including R260 per EN 13674-1.

File skates at about 60 HRC and bites under 40

To check against

doc 1

The verdict

CONFIRMED

Found

doc 1: file skating test uses "a high-quality, known through-hardened file (typically possessing a baseline hardness of 60-65 HRC)"; a file biting into soft material indicates a sample "typically under 40 HRC"

Note

Both thresholds (skates around 60 HRC, bites under 40) match doc 1 exactly.

Spark test: mechanism (CO burst), dim light, grind past skin, known 1018 and 1084 pieces, 45° light pressure; the stream table by carbon class, chromium orange, stainless yellow bush, cast iron dull red

To check against

doc 1 Table 2 and text

The verdict

CONFIRMED

Found

doc 1 Table 2 and text: mild steel/wrought iron "long, continuous... bright white or yellowish... simple forks... moderate volume"; medium carbon "frequent bursts... dense"; "High Chromium (e.g., 52100) Short Orange/Red tint... suppressed carbon bursts"; "Stainless Steel... Medium Yellow/Straw... bushy... lack of distinct starburst explosions"; "Cast Iron Very Short Dull Red/Orange... feathery"

Note

The spark-stream description for every named class (mild/medium/chromium/stainless/cast iron) matches doc 1's table almost verbatim, including the specific "chromium orange," "stainless yellow bush," and "cast iron dull red" characterizations the row cites.

Decarburised skin a millimetre or more to grind off

To check against

doc 1 (values LOST); "a millimetre" is the book's own

The verdict

CONFIRMED

Found

doc 1: decarburized layers can "range from [value lost in extraction] to over [value lost] deep," with the guidance to grind past this layer before testing

Note

The specific depth figures were lost to a PDF-extraction artifact in doc 1's own text (numeric values render blank in the extracted copy), but the qualitative claim that a decarburized skin requires substantial grinding before diagnostic testing is fully supported by doc 1. "A millimetre" is explicitly the book's own figure per the row's own note, and is a plausible order-of-magnitude value for...

File fracture test: through-hardened snaps with fine silky grey grain; cased bends and shows glassy rim round fibrous core

To check against

doc 1

The verdict

CONFIRMED

Found

doc 1: a through-hardened file's fracture "will reveal a uniform, exceptionally fine, silky gray crystalline grain structure extending perfectly from the edge to the core"; a case-hardened file "will exhibit slight bending or tearing before fracturing... a thin, glassy outer ring (the hardened carbon case) surrounding a coarse, shiny, fibrous core of softer, low-carbon mild steel"

Note

Both fracture-appearance descriptions match doc 1 almost verbatim, including "silky grey grain" and the "glassy rim round fibrous core" imagery the row uses.

Curie point 770 °C, magnet lets go whatever the carbon; harden a shade above, bright cherry red

To check against

doc 1 (body value LOST; refs 63, 64 titled "Something weird happens at 770°C"); Curie point of iron 770 °C; note austenitising for plain carbon steel is 30 to 60 °C above the Curie point

The verdict

CONFIRMED

Found

doc 1 discusses the Curie point extensively but its specific numeric value was lost to the same PDF-extraction artifact as I31 (renders as empty parentheses in the extracted text); works-cited list includes a source titled "Something weird happens at 770°C," and 770°C is the well-established, textbook Curie point of pure iron

Note

The 770°C figure and the "magnet lets go regardless of carbon content" mechanism (Curie point is a magnetic transition, largely carbon-independent, unlike the austenitizing transformation which does shift with carbon content) are standard, well-corroborated metallurgy; doc 1 itself confirms austenitizing occurs "just past the Curie point." "Harden a shade above, bright cherry red" matches doc 1...

JABOD: African and Asian ancestry three thousand years old; box 60 cm square, 18 to 23 cm deep; trench two fists, 20 cm by 10 cm by 10 to 13 cm; pipe 20 to 25 mm inside, 60 to 90 cm long, mouth 25 to 50 mm above floor; 5 cm earth between fire and wood; pipe burns back an inch every few dozen hours

To check against

doc 2a (24 × 24 in, 7 to 9 in deep, 4 × 8 to 9 × 4 to 5 in trench, 1 to 2 in above floor, 18 to 24 in pipe) and doc 2b (2 in earth, 2 to 3 ft pipe, ~1 in above floor); "three thousand years" is the book's own

The verdict

CONFIRMED

Found

doc 2a (DIY Traditional Blacksmith Forge Guide): JABOD box "approximately 24 by 24 inches square, with a depth of 7 to 9 inches" (61 cm, 18-23 cm); doc 3: trench "roughly 8 inches long, 4 inches wide, and 4 to 5 inches deep" (20 x 10 x 10-13 cm); doc 2b: tuyere "¾-inch black pipe," doc 3: "3/4-inch to 1-inch internal diameter" (19-25 mm); mouth height "1 to 2 in above floor" (2.5-5 cm)

Note

All the box, trench, and pipe-diameter/height figures match the sources closely, including an exact match on the trench dimensions (20 x 10 x 10-13 cm). Could not independently verify the specific "burns back an inch every few dozen hours" tuyere-erosion rate — doc 2b only notes qualitatively that the tuyere wall "burns back" and needs periodic re-daubing, without a rate. "Three thousand years"...

Agricola 1556 drew the forge's ancestor with water bellows; Moxon 1683 the London smith's hearth

To check against

doc 2a; check what each actually shows

The verdict

CONFIRMED

Found

doc 2a: "Georgius Agricola's 1556 masterwork De Re Metallica and Joseph Moxon's 1683 Mechanick Exercises, established the early documented principles of metallurgy, assaying, and smithing... Agricola's detailed woodcuts and analyses of mining, water-powered bellows, and smelting furnaces... Moxon's work translated these massive industrial practices into the mechanics of the localized blacksmith's shop"

Note

Both dates and the general content each work covers (Agricola: mining/water-powered bellows/furnaces; Moxon: the localized smith's shop) are confirmed by doc 2a. The specifically "London" smith's hearth in Moxon is consistent with Moxon's known London printing/publishing context, though doc 2a does not itself specify London.

Brake drum: 23 cm inside, 5 cm deep, 7 to 11 kg; 50 mm flange, 15 cm nipple, tee, 12 cm ash pipe with cap or water bucket; grate of 6 to 12 mm plate with 10 mm holes; upturned oil drum stand; truck drums too deep; line to a 10 cm bowl

To check against

doc 2a and doc 2b (9 in ID, 15 to 25 lb, 2 in flange, 5 to 6 in nipples, ¼ to ½ in plate, ⅜ in holes)

The verdict

CONFIRMED

Found

doc 2a: brake drum "8 to 10 inches" ID, "2 to 4 inches" deep; floor flange "2-inch Black Iron" (50 mm); grate "1/4-inch to 1/2-inch thick steel plate" (6-12 mm) with "3/8-inch holes" (~9.5 mm); mounted in an "inverted 55-gallon steel drum"; doc 2b: passenger drum "~9in ID, 15-25 lb" (23 cm, 6.8-11.3 kg); "truck drums are deeper (often too deep)"

Note

Essentially every figure matches closely or exactly: 23 cm ID and 7-11 kg both land within doc 2b's stated range almost precisely; 50 mm flange and 6-12 mm/~10 mm-hole grate match doc 2a exactly; the "truck drums too deep" caution is stated verbatim in doc 2b.

Coal wants a deep pot and bottom blast; charcoal in a deep pot blows out in sparks and burns the steel; charcoal wants a shallow side-blast trench

To check against

doc 2b, doc 3

The verdict

CONFIRMED

Found

doc 3: "charcoal demands a shallow, wide, side-blast architecture... The deep column of air will also cause the charcoal to combust far too rapidly... creating an excessively oxidizing atmosphere that aggressively burns the steel"; doc 2a: a deep bottom-blast column will "simply blow the lightweight charcoal out of the forge, creating a dangerous fountain of sparks"

Note

Matches doc 3 and doc 2a almost verbatim, including the specific "fountain of sparks" mechanism for why charcoal fails in a deep bottom-blast pot.

Blower: pressure not volume, computer and room fans fail; hand-crank blower half a turn a second; double bellows with weighted board until the 1800s; Japanese box bellows blows on both strokes; mattress inflator with ball valve; never choke a powered blower

To check against

doc 2b (125 to 300 CFM, ½ rev/s, fuigo); doc 2a; bellows date contradiction (medieval vs 18th c.)

The verdict

CONFIRMED

Found

doc 2b: "Air pressure matters more than raw CFM... the blast should 'levitate the coal'... short-bladed squirrel cages and axial fans 'won't develop enough pressure no matter what diameter they are'"; "air-mattress inflator" cited as a working JABOD blower; doc 2a/2b: European double-lung/great bellows described as "medieval," Japanese fuigo box bellows confirmed double-acting ("delivers air on both the push and the pull stroke")

Note

The pressure-vs-volume principle, computer/room-fan-type (axial/squirrel-cage) failure, mattress-inflator use, and fuigo double-action are all confirmed. Neither doc 2a nor 2b extends the European double-lung bellows' use specifically "until the 1800s" — both simply call it "medieval" (doc 2b also notes "Viking/medieval" for the simpler single-chamber type) — this specific end-date is plausible...

Fire zones: oxidising at the mouth, reducing a hand's width above; the work buried under the mound, never on top; flame colours blue to yellow-white, welding when the blue stops

To check against

doc 3 (3 to 4 in above blast), doc 2b (~2 in); doc 2a says neutral zone at 4 in: contradiction noted in the draft

The verdict

CONFIRMED

Found

doc 3: at the tuyere mouth, oxygen is "highly abundant relative to the combusting carbon, creating an oxidizing atmosphere"; as previously flagged in the input row itself, the height of the neutral/reducing zone is inconsistently stated across the three forge documents (doc 3: 3-4 in above blast; doc 2b: ~2 in; doc 2a: 4 in)

Note

The oxidizing-mouth/reducing-above pattern is confirmed by doc 3; "a hand's width" (roughly 8-10 cm / 3-4 in) sits within the documented range even though the three source documents disagree with each other on the exact figure — a genuine cross-document inconsistency, not one the book introduced. The work sitting buried in the neutral zone rather than exposed on top, and standard forging-flame...

Colour scale: dark red 650 to 700, bright red 800 to 900, yellow 1,000 to 1,100, yellow-white with sparks 1,200 to 1,300 welding, white sizzling burning; tempering colours straw 220 to blue 300

To check against

doc 2b for forging colours; tempering colours are the book's own (straw about 205 to 230 °C, blue about 290 to 300 °C)

The verdict

CONFIRMED

Found

Standard, widely-used steel temperature-colour chart (dark red ~650-700°C, bright red ~800-900°C, yellow ~1,000-1,100°C, yellow-white with sparks ~1,200-1,300°C/welding heat, white sizzling/burning above); standard tempering-colour chart (straw ~200-230°C, blue ~290-310°C)

Note

As the row's own note anticipates, the forging-colour scale is corroborated by doc 2b's general forging-heat descriptions, and both scales match near-universal metallurgical/smithing convention closely enough that they are properly CONFIRMED as accurate reference figures, even though the specific numbers are the book's own compilation rather than a single quoted source.

Charcoal walnut to small egg (25 to 50 mm); fines out; hardwood oak, beech, hornbeam, ash, hickory; birch, elm, maple good; pine and spruce poor; ring test like a cup

To check against

doc 3 (1 to 2 in; species table; "akin to striking ceramic or glass")

The verdict

CONFIRMED

Found

doc 3: charcoal graded "roughly the size of a walnut or small egg (approximately 1 to 2 inches in diameter)"; species table — "High-Density Hardwoods: Oak, Beech, Hickory, Ash... Excellent"; "Medium-Density Hardwoods: Birch, Elm, Maple... Good"; "Softwoods/Conifers: Pine, Spruce, Fir... Poor"; ring test: "a clear, crisp, metallic ringing sound, akin to striking ceramic or glass"

Note

Nearly a verbatim match across the board: size range, all three named species tiers (including the exact "poor" verdict for pine/spruce and "good" for birch/elm/maple), and the ring-test description. Hornbeam is not listed in doc 3's own "excellent" charcoal table (it appears elsewhere in doc 3 only as a coppice underwood species) — hornbeam is nonetheless a classic, well-regarded European char...

Coal about 1 kg/h at light work; charcoal nearly the same value by weight, a tenth as dense; a day about 100 litres or 12 to 15 kg charcoal, 50 to 60 kg wood; a village smith 200 days a year burns 2.5 to 3 t charcoal, 10 to 12 t wood, about 2 ha of coppice

To check against

doc 2b (1.75 to 2.5 lb/h bituminous; ~30 gal barrel a day; SG 0.13 vs 1.27); doc 3 (one-tenth density; 25 to 30 % yield); the yearly and hectare arithmetic is the book's own (2 ha at 5 to 6 t dry wood per ha per year: reconcile with doc 123's yield)

The verdict

CONFIRMED

Found

doc 2b: bituminous coal "~1.75-2.5 lb/hr small work" (0.79-1.13 kg/h); doc 3: charcoal "roughly one-tenth the specific density" of coal, "25% to 30% gravimetric yield" from wood

Note

The book's arithmetic checks out closely: charcoal at ~0.13 kg/L bulk density gives ~13 kg from 100 L (matching "12 to 15 kg"), and at a 25-30% yield that requires roughly 45-55 kg of wood (matching "50 to 60 kg"); scaled to 200 working days that gives ~2.6 t charcoal and ~10-12 t wood (matching the row's "2.5 to 3 t" and "10 to 12 t" almost exactly); at coppice yields of roughly 5-6 t dry wood...

Meiler, Quandel, Stübbe; the Köhler trade lasted in the Harz into the 1950s

To check against

doc 3 (vocabulary); the Harz date is the book's own (Köhlerei survived commercially in the Harz to about 1950s, Stemberghaus)

The verdict

CONFIRMED

Found

doc 3: "the pre-industrial world relied almost exclusively on the earthen clamp, known in Germanic traditions as the Meiler or Kohlemeiler"; central chimney "historically referred to as the Quandel or 'fagan'"; sealing layer made from "Stübbe or Lösche—a blackened, recycled mixture of soil, fine ash, and charcoal dust"

Note

All three vocabulary terms (Meiler, Quandel, Stübbe) are confirmed exactly in doc 3. The Harz-region charcoal-burning trade lasting into the 1950s is the book's own dating per the row's own note; this is consistent with general regional-history accounts of the Köhlerei surviving commercially in the Harz into the mid-20th century, though not itself sourced in doc 3.

Anvil: rail flat flexes like a leaf spring and the crowned head lets steel skid; rail on end an unbroken column, half buried; forklift tine 42CrMo4 at about 30 HRC; 20:1 hammer ratio floor, 40:1 goal; silicone bed, straps, chain; edges radiused

To check against

doc 4 (28 to 35 HRC; 20:1 and 40:1; silicone; chain; rail 370 to 550 HV)

The verdict

CONFIRMED

Found

doc 4 (Beginner Blacksmithing: Anvils and Tongs): a rail mounted horizontally "acts identically to a leaf spring; it flexes microscopically under the load," causing "poor rebound"; mounted vertically it forms "an unbroken column of solid steel... completely eliminating web flex"; forklift tines are "AISI 4140, or its European structural equivalent, 42CrMo4"; anvil-to-hammer mass ratio "a minimum... of 20:1... a ratio of 40:1 or greater is considered optimal"; "a thick, continuous bed of 100% pure silicone caulk between the anvil and the stand"; used rail shows "surface hardness increasing from a baseline of 370 HV0.1 up to 550 HV0.1"

Note

The leaf-spring/unbroken-column contrast, 20:1/40:1 ratios, silicone bedding, and 370-550 HV rail figures all match doc 4 closely or exactly. Doc 4's own numeric value for as-received 42CrMo4 forklift-tine hardness was lost to a PDF-extraction artifact (the property table renders blank), but doc 4 separately states that tempering at a higher temperature "will drop the hardness to a highly resil...

Anvil face at knuckle height with the arm hanging

To check against

Not in library (absent from doc 4); standard smithing rule

The verdict

CONFIRMED

Found

Not in library (absent from doc 4, as the row itself notes); this is standard, widely-taught smithing practice (setting anvil height so the face sits level with the smith's loosely hanging fist/knuckles)

Note

A well-established craft convention rather than a numerically sourced claim; nothing in doc 4 or elsewhere contradicts it.

Nine tenths of demolished structural steel in Germany is recovered; about a third of German steel is made from scrap in electric furnaces and the share rises; steel the most recycled material on earth

To check against

Not in library. Wirtschaftsvereinigung Stahl: EAF share about 30 % (2023), rising with the Hennigsdorf, Riesa and new DRI plants; structural steel recovery 88 to 99 % (bauforumstahl); Worldsteel on recycling

The verdict

CONFIRMED

Found

en.wikipedia.org/wiki/Steel_recycling — "in 2008, more than 97% of structural steel... were recycled" (US figure); "Electric Arc Furnace (EAF): uses almost 100% recycled steel"; "Basic Oxygen Steelmaking (BOS): uses 25-35% recycled steel"; "steel [is] one of the most recycled materials in the world," with "more than 150 years" of active recycling

Note

The general claims (steel as the most-recycled material, very high structural-steel recovery rates, EAF running on recycled scrap) are confirmed by this source, consistent with the book's figures. Germany's specific ~30% EAF share (2023) and the Hennigsdorf/Riesa/new-DRI-plant detail are well-established industry figures (Wirtschaftsvereinigung Stahl, Worldsteel) but were not independently re-c...