Wheal Martyn Clay Works

Chi­na clay is mined in Corn­wall around St Austell. Wheal Mar­tyn Clay Works muse­um gives a won­der­ful jour­ney through the old indus­try, with the sur­prise of see­ing a huge mod­ern pit still oper­at­ing at the end. It also shows many oth­er aspects of ceram­ics and pot mak­ing. This is must see vis­it if in the area and is fam­i­ly friend­ly too.

The muse­um tells the sto­ry of chi­na clay back­wards, tak­ing vis­i­tors from the bot­tom of the hill where the clay was despatched, work­ing upwards through var­i­ous set­tling and dry­ing pans, to the top of the hill and spec­tac­u­lar views of the work­ing clay pit. It is laid out in this way because water and grav­i­ty were so much used in the clay clean­ing process. For clar­i­ty this arti­cle will look at the process from get­ting the raw mate­r­i­al and on through the process of refin­ing to end up with chi­na clay.

Background

The 18th cen­tu­ry saw Euro­peans con­sumed with a lust for the ceram­ics import­ed from Chi­na. This set in motion in an intense hunt for white­ness and translu­cen­cy in ceram­ics. The dis­cov­ery of a clay -‘chi­na’ clay — made this pos­si­ble through the devel­op­ment of Euro­pean porce­lains and oth­er white clay bodies.

Chi­na clay is known by pot­ters as a pri­ma­ry clay, mean­ing it has­n’t moved posi­tion by water or wind ero­sion and so remains very pure. Notably, it has­n’t picked up lots of iron caus­ing it to fire to a brown colour, nor have the clay par­ti­cles been ground down to make it plas­tic and low­er it’s melt­ing point, which is the case with sec­ondary clays. Cor­nish chi­na clay is decom­posed gran­ite and sits where it was cre­at­ed, amongst gran­ite pieces and has to be washed out by water.

Monitors

By the 1920’s they were blast­ing the rock with water canon called monitors.

Pumps and drive mechanisms: water wheel and flat rods

As pits were dug and water blast­ed down, the clay slur­ry had to be pumped from the bot­tom of the pits up to a height which allowed it to flow down towards a vari­ety of set­tling tanks, where the the mica and gran­ite stones were sep­a­rat­ed from the clay and the clay was dried. In the ear­ly days, pow­er to the pump was sup­plied by a water wheel, posi­tioned some dis­tance away. A com­pli­cat­ed series of rods was devised to get the pow­er from the water wheel to the pump.

Water wheel

Flat rods

Flat rod tunnel

Plunger pump

Plunger pumps like this below, were devel­oped by Richard Tre­vithick for the tin and cop­per mines in Cornwall.

Slurry flowing down the hill

Adit or level

The mouth of a tun­nel is an adit (or lev­el), which car­ried clay slur­ry from the mine face to the drags fur­ther down the hill.

Drags

The slur­ry is pumped into these “drags”, which are troughs with a very grad­u­al­ly slope to them. The slur­ry moves slow­ly through them, allow­ing the sand and mica time to set­tle out. Only water and chi­na clay flow over the top of the end of the trough. The drags had to be cleaned of sand around every eight hours. It was washed away down into the riv­er below and then to the sea.

Settling pit and tanks

The pure chi­na clay and water mix set­tles in pit, with the clear water run­ning off the top until, after a few days, a con­sis­ten­cy of sin­gle cream is achieved, when it went to anoth­er set­tling tank. 

The final set­tling tank before it goes into the pan kiln. Inci­den­tal­ly, the hill in the back­ground is man-made. It is a tip made from the grav­el set­tled out dur­ing the chi­na clay min­ing process.

Pan kiln, locally known as ‘the dry’

Dry­ing the chi­na clay prop­er­ly proved dif­fi­cult in Corn­wal­l’s damp cli­mate, so sheds with under­floor heat­ing were intro­duced. The chi­na clay slur­ry was spread over the floor and then cut into liftable blocks when it is dry enough to remove.

You are giv­en a new under­stand­ing of the land­scape around St Aus­tel after a vis­it to this great museum.