SECT. IX.
Trewteft
Clay.
ipgpper-cprn, and plainly, & dohgferiest'of fmg$ter>~ dryftals/ cemented
together, into a lump: their 'an|*lg§ were lonjewhat blunted^htit the
fmaller gravels or fapds were quite (angularif* mixed with jtfte; gravely
Was a good deal o f lpafy talc, which, in the 'micrafcopc, ajes
peared as jfo mapy lamince, oCq^ftal.r>. «ufThe three eighths ■ fuf-/«
pended in the water, and left to fettle, depofited an; exceeding white
clayV.it whitens' the fingers, ,flicks tofthe .tofigoe,[extremely
finooth tehrfre touch, taftlefs*- a (little grftj^ub'efween« thfeyitefith,'
owing to the finaller grains of talc,', which nev-ef - defend the'Clay
during t&p depuration. Being of lb fair a=e^|l(|it|> I groundifom^pf
it with nut oil, . but it loft its 'whiteneiS, and became fat, and of a
dove colour': with linfeed oil it» grew much more yellow* lb -,thajt
ft wm. not, as ajcolour, be fit'for painters;- jwth aqua.yfqrtis^ijt
makes not the leaft effervefcence, but refolves' into a pafte*; put into;
a fierce fire, arid kept there , four hours ^aftd^forty'itxifisu^^ it neither
vitrified nor altered its colour*, -and "acquired nQ)'|hj|te hardnels*
than is neceflary for'paftils for drawing. As this Glay^fbparates fo
eafily from its land, has much talc, (and therefofelwill not yitrii^)’
and the pureft colour, it may poilibly, both .»without yas?welh as
Wipi its fand, upon different occafions, Ip ^ v e ry ufefuki&gireda’elt:
for making porcelain; at prefent,- in its natural ftate, OTf^es, oidys
to make bricks for fmelting-houfes, enduring the inaqftcdntenfe fire;,
oF the furnace better than any othei: within *agnaL reach ,o£~the
workmen. By its diflolving lb- readily in wafer, - itm ^ ib e a kind
o f marie, and ufeful as a manure.
There is a Jiratum o f elay not very different from Mie foregoifig
in the tenement of Trewren* in the parifh, o f Madern ■: ilt fefifts toe>
fire well, and is ufed by the melters -foS? the fameJ-purpbfeJtas - that
above, but is not near lb white, fmooth, and^ ftiy by 'burning a'
final! quantity of it* it appears more tenacious, r-and fitter fdr ftone
and potters ware, being reduced inton very hard clomevby myffudy
fire. There are many other whitifh GlayS 5^iri;'Cornwall o f much
the. lame nature as thole already mentioned. I have-only to remark,
that in the heart of the bed of clay found at Amelebreh,. them are
lome fcattered ftony glebes of red earth, like the Rubrica of Plifty,
and the Miltos of the Greeks. I immerled this ruddle ;|tit water,
but it would not diflolve: upon grinding it,^ the ftony part was
hard and gravelly, but being well ground down with clarified
linfeed oil, it made’ a very good red, and mixed kindly with
white, making a good flelh colour, and though laid on thick on;*
the canvas, would not ftart, nor alter its colour; fo that a better
m As at Tregonin Hill in Breag, at Treaflb in Ludgvan, in the parifh of St* Enodor, and near the
town of Loftwythyel, See*
red
ip fa tfa ,%Otpurpofes redjjPbMe,) canqot well bp^e^og^-d 'tq,
groupd,, It rnayfefeqnjffofmewhat ftrange thaj: glebes
? f|?Ejr,th;| be foundffcatfie^d in k. body
of clayro white a,ndj||^q; biflJ|feure, ^as; welffuiidef, ground as
Sove;,. it ftill various j^and- th£7more ^ e , wpfecpt'e ou^refearches,
tho?jm|rer fnhjefif^.we may expJlLto meet with which will excite
ouij i admiration, f and scgp^nce us<> q£ qur*.('fgno:rancp. i One thing
hoyyeyer ma^fe^fervedH thati tjp|fe|, red< and are vem
different in n a t u r e , a s . red,;,fnixing weE "
wi|h_oil, ancy ^ t |wi,tiru water ; the,pother;, as; grfeedilyi '.imbibing
water,fiand, pqtjm^i|tg^oil,, If tthqfe fq different fubftahceslhere-
fore an?e now found,tin^tftep oriV S B edsyla1», is. moil likdy^tne red
muftjhave been repelled^oi^ all* fidpt white,'and ppmpadted
tpget^jsr ,byidile‘jattra.dion o f its, own fimilar jlarts.
In thq .parifh oV,?|^^Yr|n jheje 'ib adyd^wjel^Kyhich, ror t-ECT.x.
caftingsfilver, ,brafs,,;orlead, is( reckoned to;e|eeed every thing of qV 67” "
fits? kind in-thefe ,pajjts.
g^pln^the parifh of Tannant. there is a^yellow; clay much, coveted'for sect, x i
building furnaces : ’tis carried off to Briftql f and Wales, and othei; tamant
places;, in fuch quantities ..every -»year, that Humphry, Mackwoijth. ChT‘
Praed, yEifq; owne%>of the naakes above ioq| pounds’
qmmm of this clay, «72««; and from January 1757, f>,
to Midlummer following, received for it 150 pounds.. .Bricks..
made of this clay melt and vitrify in th| ^nre, running’ t iiftb’.qne
iblid body ; but afterwards never ftir till quite .caloined', enduring
tfte moft intenfe fire beyond any bricks ufed for, like purpofes.
There is a yellow fandy clay injthe^orlas, near thp Long Bridge, sect.xh.
in the parifh of Ludgvan, gopd for bricks and plaifter; and in feme Ludgvan
parts of the fame pit, a fine blue clay, which, being well mixed with Clay‘
white, (fuch as the Amalebreh before-mentioned) makes an excellent
lute for affcvmg.f c f f l js blue clay vitrifies. prefendy, but the
white will lcarce vitrify at a ll; neither of thele clays is therefore
proper for luting the crucible feparately taken,'but mixed they correct
one another, and there is no better compofitiqn for. the aflay furnadd
Near the borough of Lifkerd there is.fopnd in, gteat ^plenty a sect, xhr
yeUow flatty clay of,a fine eartfulit feels and. puts finooth, and with a cV
good polifh, and the colour was as fine' fo the e yq^ tn e Naples
y ellow ^ but, upon tryal, it'vfeould not-mi£ with ,pi|f it grew fat
and greafy ; it is (ftextfore a fteatitfes. " It is good for grafs; for a.
gentleman
* A light beaatifyl .yeHow earth, macb eftesmed. in painting, ’v