Thesamerestrictionsalikeaffectedtheoperationsoftheglassmanufacture，which，withtheaidofforeignartisans，hadbeengraduallyestablishedinEngland，andwasbecomingathrivingbranchoftrade。Itwasevenproposedthatthesmeltingofironshouldbeabsolutelyprohibited：”manythink，”saidacontemporarywriter，”thatthereshouldbeNOWORKSANYWHERE——theydosodevourthewoods。”
Theuseofiron，however，couldnotbedispensedwith。Theveryfoundationsofsocietyresteduponanabundantsupplyofit，fortoolsandimplementsofpeace，aswellasforweaponsofwar。Inthedearthofthearticleathome，asupplyofitwasthereforesoughtforabroad；andbothironandsteelcametobeimportedinlargely-increasedquantities。ThisbranchoftradewasprincipallyinthehandsoftheSteelyardCompanyofForeignMerchants，establishedinUpperThamesStreet，alittleaboveLondonBridge；andtheyimportedlargequantitiesofironandsteelfromforeigncountries，principallyfromSweden，Germany，andSpain。ThebestironcamefromSpain，thoughtheSpaniardsontheirpartcovetedourEnglishmadecannons，whichwerebettermanufacturedthantheirs；whilethebeststeelcamefromGermanyandSweden。*
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Aslateas1790，longafterthemonopolyoftheforeignmerchantshadbeenabolished，Pennantsays，”ThepresentSteelyardisthegreatrepositoryofimportediron，whichfurnishesourmetropoliswiththatnecessarymaterial。Thequantityofbarsthatfillstheyardsandwarehousesofthisquarterstrikeswithastonishmentthemostindifferentbeholder。”——PENNANT，AccountofLondon，309。
Underthesecircumstances，itwasnaturalthatpersonsinterestedintheEnglishironmanufactureshouldturntheirattentiontosomeotherdescriptionoffuelwhichshouldserveasasubstitutefortheprohibitedarticle。Therewasknowntobeanabundanceofcoalinthenorthernandmidlandcounties，anditoccurredtosomespeculatorsmorethanusuallydaring，toproposeitasasubstituteforthecharcoalfuelmadefromwood。Butthesamepopularprejudicewhichexistedagainsttheuseofcoalfordomesticpurposes，preventeditsbeingemployedforpurposesofmanufacture；andtheywerethoughtveryfoolishpersonsindeedwhofirstpromulgatedtheideaofsmeltingironbymeansofpit-coal。Theoldmanufacturersheldittobeimpossibletoreducetheoreinanyotherwaythanbymeansofcharcoalofwood。Itwasonlywhenthewoodintheneighbourhoodoftheironworkshadbeenalmostentirelyburntup，thatthemanufacturersweredriventoentertaintheideaofusingcoalasasubstitute；butmorethanahundredyearspassedbeforethepracticeofsmeltingironbyitsmeansbecamegeneral。