Keep­ing sharp

The need for a sharp­en­ing stone sends this writer off on an in­ter­est­ing quest

The Shed - - Contents - By Ritchie Wil­son Pho­to­graphs: Ritchie Wil­son

Iwanted a nat­u­ral sharp­en­ing stone and didn’t want to pay for a Ja­panese wa­ter stone, many va­ri­eties of which I have seen for sale in Ja­pan. Some of th­ese cost more than $100. Arkansas and Washita stones from Amer­ica are sim­i­larly pricey.

I came across a ref­er­ence to Māori us­ing stone from Lyt­tel­ton Har­bour for sharp­en­ing and I thought that I could col­lect a stone from their old quarry, shape and flat­ten it, and I would be in busi­ness — and my cash would stay safely in my wal­let. It was while I was try­ing to get more in­for­ma­tion about lo­cal sharp­en­ing stones that I was struck by the sim­i­lar­i­ties be­tween sharp­en­ing steel and stone tools. Both use abra­sives to wear away two flat sur­faces that meet at the cut­ting edge.

First Kiwi-made tools

For the early Poly­ne­sians, ar­riv­ing at a new, pre­vi­ously un­in­hab­ited Pa­cific is­land would have been like be­ing given the keys to Pak ’n’ Save. Large flight­less birds and plen­ti­ful sea mam­mals, with no fear of hu­mans, would have pro­vided easy eat­ing for gen­er­a­tions. Be­cause of the typ­i­cally very long voy­ages un­der­taken to find new land, re­plac­ing stone tools as they wore out or broke was not so easy. They had to do it them­selves us­ing the ma­te­ri­als at hand. In the South Pa­cific and Hawaii the best ma­te­rial was the vol­canic rock, basalt, of which the is­lands were com­posed. When Māori ar­rived in Aotearoa 800 years ago, they would have been eval­u­at­ing the stone out­crops’ potential for tool­mak­ing and tool sharp­en­ing from the very first. 

Ob­sid­ian — a per­fect knife

It is thought that th­ese first ar­rivals to New Zealand were very ac­com­plished sailors, so they had the mo­bil­ity to quickly ex­plore their new home and iden­tify suit­able tool­mak­ing stones in many, es­pe­cially coastal, places.

They soon dis­cov­ered the vol­canic glass ob­sid­ian, called ‘matā’ by the Māori, at sev­eral sites — the best came from Mayor Is­land in the Bay of Plenty. Ob­sid­ian was val­ued be­cause frag­ments nat­u­rally have very sharp edges, which make them use­ful as knives. Larger blades for the very im­por­tant wood­work­ing adzes were hard to make from ob­sid­ian and many dif­fer­ent stones were used for this pur­pose. The fine­grained basalt from the Coro­man­del re­gion was pre­ferred in the early days of Māori set­tle­ment. Later, the hard, grey sand­stone greywacke, of which the South­ern Alps are made, was most com­monly used, al­though the supreme neph­rite — pounamu — from the Arahura and Tara­makau Rivers on the West Coast of the South Is­land, was most val­ued.

The need for sharp­en­ing

Adzes (toki) and chis­els (whao), what­ever they are made from, have to be sharp to cut wood. Māori used ei­ther a mix­ture of sharp sand and wa­ter on a hard, flat stone, or a flat piece of wet­ted

sand­stone, to sharpen and pol­ish stone tools. Ev­i­dence of the use of sand­stone out­crops for this pur­pose can still be seen at some lo­ca­tions, usu­ally very near to wa­ter. Sand and sand­stone are both a re­sult of the weather­ing of quartz. The small, hard, sharp-edged sil­ica crys­tals, made by the break-up of lumps of quartz, scratch the stone be­ing sharp­ened, abrad­ing it away. The fi­nal pol­ish was achieved by us­ing red ochre (kokowai), which con­tains rouge, ap­plied with, per­haps, an­i­mal skin. Traces of the red, very fine abra­sive can be seen on some toki.

What­ever they are made from, [they] have to be sharp to cut wood

Steel ar­rives

Con­tact with Euro­pean sailors re­sulted in ma­jor changes to the tools of the Māori long be­fore any sig­nif­i­cant im­pact was felt in other as­pects of tra­di­tional Māori life. Carvers made in­creas­ing use of steel chis­els made from nails. Adze blades were made first from bar­rel hoops, then from cut­ters from car­pen­ter’s planes, and fi­nally were largely re­placed by Euro­pean adzes and axes.

The stone adzes were then used for gar­den­ing; aban­doned; or, if pounamu, re­shaped into hei tiki. Stone adze heads are con­tin­u­ally be­ing dis­cov­ered and handed into our lo­cal mu­se­ums.

Th­ese new metal tools were sought after by Māori be­cause metal makes a more durable cut­ting blade that holds an edge bet­ter and is prob­a­bly sharper too, but sharp­ened in the same way as stone blades.

The cut­ting edge of a metal tool is also formed by the grind­ing of two sur­faces that meet at a line. Again, small, hard, sharp crys­tals are used to scratch the metal to make the flat sur­faces. The harder the crys­tals, the harder the metal that can be sharp­ened. The smaller the crys­tals, the finer the scratches and the sharper the edge. The larger the crys­tals, the faster the edge is sharp­ened.

Hard, crys­talline ma­te­ri­als

When we look at a list of hard crys­talline ma­te­ri­als, we see many of the sub­stances that we use for sharp­en­ing in the shed. Di­a­mond, silicon car­bide (car­borun­dum), sil­ica (sand), alu­minium ox­ide (alu­mina), rouge (iron III ox­ide), and glass are all used as abra­sives and all sharpen in the same way as the sand slur­ries of pre-Euro­pean Māori.

Be­fore the last cen­tury wa­ter stones were the usual sharp­en­ing ma­te­rial. Th­ese were made of sand­stone, which is a sed­i­men­tary rock con­sist­ing of sil­ica crys­tals that have been bonded to­gether by heat and pres­sure deep be­neath the Earth’s sur­face. The hard sil­ica crys­tals on the face of a wa­ter stone re­moved metal from the sur­face be­ing sharp­ened and plenty of wa­ter kept the metal cool and washed away the mix­ture of lost metal par­ti­cles and detached, bro­ken sil­ica crys­tals called ‘swarf’. This al­lowed new sharp crys­tals to be un­cov­ered and brought into ac­tion. As the stones were used they were worn away and stopped be­ing flat and so had to be flat­tened us­ing a flat, hard rock and a sand slurry — just as the Māori did.

Wa­ter stones revered

The best wa­ter stones were highly val­ued, as they con­tinue to be to­day, and were traded widely around the world. The first Euro­peans to set­tle in New Zealand would have brought a wa­ter stone in their swag as well as the classic axe and a Bi­ble. If they were English the stone would have prob­a­bly been a Charn­wood For­est stone from Le­ices­ter­shire, but there would have been a va­ri­ety to choose from — some,

such as Turkey stones, from as far away as Le­banon and Syria. Māori called wa­ter stones ‘hōanga’, and an ex­am­ple of th­ese was a sand­stone from tiny King Billy Is­land in the South Is­land’s Lyt­tel­ton Har­bour. Some hōanga were so revered that they were named and had sto­ries com­posed about their his­tory. One fa­mous ex­am­ple near Ro­torua was said to have been brought from Poly­ne­sia on the Arawa waka.

Finer abra­sive oil stones

Un­til re­cently, oil stones, con­sist­ing of silicon car­bide crys­tals of a uni­form size em­bed­ded in a bond­ing agent, were uni­ver­sally used by work­ers in West­ern coun­tries to keep a sharp edge on tools. Be­ing man­u­fac­tured, oil stones were rel­a­tively cheap and con­sis­tent. The ‘oil’ in the name refers to the light

min­eral oil which was used on the stone to lubri­cate and cool the abra­sive and to al­low swarf to be moved away from the sharp­en­ing sur­face. Oil stones are also com­monly made from alu­minium ox­ide (alu­mina), which has gen­er­ally finer abra­sive par­ti­cles and so pro­duces a sharper edge more slowly. Th­ese are called In­dia stones. Some nat­u­ral stones, such as Arkansas stone from Amer­ica, are also used as oil stones but are much more ex­pen­sive.

Di­a­mond days

The se­ri­ous wood­worker of to­day would almost cer­tainly use di­a­mond as a sharp­en­ing ma­te­rial. Di­a­mond is so hard that it is worn away by sharp­en­ing much more slowly than other abra­sives, so only one layer of di­a­mond is used. This is bonded to a (hope­fully) flat sur­face that in­cor­po­rates de­pres­sions to re­move swarf so that the di­a­mond crys­tals aren’t clogged with metal par­ti­cles. Us­ing the plate wet ap­par­ently makes it last longer.

The di­a­monds used are rel­a­tively in­ex­pen­sive be­cause they are man­u­fac­tured. They are sorted by size so that di­a­mond plates of var­i­ous coarse­ness, al­though not very fine, can be pro­duced. Di­a­mond plates are un­ri­valled in re­mov­ing metal quickly and in sharp­en­ing very hard al­loys like high­speed steel, but strug­gle to pro­duce a mirror fin­ish on the tool and hence a re­ally sharp edge. Di­a­monds are also ex­cel­lent con­duc­tors of heat, so the sur­face be­ing sharp­ened shouldn’t over­heat and lose tem­per. ‘Tem­per’ is the hard­ness caused by the heat treat­ment of steel.

Ja­panese wa­ter stones

Ja­panese tools are in­creas­ingly be­ing used by both pro­fes­sional and am­a­teur wood­work­ers, as are Ja­panese wa­ter stones. Th­ese have as abra­sives the fa­mil­iar sil­ica par­ti­cles, but their dif­fer­ence is that the par­ti­cles are em­bed­ded in a clay ma­trix. This makes the stone softer than sand­stones with the ad­van­tage that new sharp­en­ing par­ti­cles are con­tin­u­ally be­ing un­cov­ered as a tool is moved over the stone, lead­ing to rapid sharp­en­ing.

The dis­ad­van­tage is that the stone wears quickly and has to be fre­quently flat­tened (or ‘trued’) to main­tain a flat sharp­en­ing sur­face. Di­a­mond plates would be suit­able for this, or spe­cial­ized flat­ten­ing sur­faces used with silicon car­bide pow­der could be used. Ja­panese wa­ter stones were orig­i­nally nat­u­ral, be­ing quar­ried at nu­mer­ous lo­ca­tions in Ja­pan, but are now mainly man­u­fac­tured, sev­eral com­pa­nies pro­duc­ing var­i­ous brands. Like other sharp­en­ing stones they come in a va­ri­ety of abra­sive par­ti­cle sizes, some of which are very fine, per­haps the finest avail­able. Finer par­ti­cles equal sharper edges but slower sharp­en­ing. Over­all Ja­panese wa­ter stones pro­vide a sharper edge for less sharp­en­ing ef­fort, which means that they can be sold at a pre­mium price.

The old name for sharp­en­ing

As a child I used to see a coun­cil worker reg­u­larly cut the grass verge of our road with a scythe. Ev­ery 10 min­utes or so he would take a round oil stone out of a leather pouch at­tached to his belt and wipe it a few times along the cut­ting edge. This process was called ‘whet­ting’, the old name for sharp­en­ing, and he would have been said to have ‘whet the edge’ of the scythe. The oil stone would have been called a ‘whet­stone’. He would have pe­ri­od­i­cally oiled the stone’s sur­face with an oil-soaked rag from the pouch. I can’t re­mem­ber him having an oil can con­cealed about his per­son; per­haps it was in an­other belt pouch. Or was it in his … Truck? Un­likely. Bi­cy­cle? Horse? It’s a long time ago. 

I was aware that get­ting a sharp­en­ing stone from tiny King Billy Is­land in Lyt­tel­ton Har­bour would be prob­lem­atic be­cause it is ad­min­is­tered by the Depart­ment of Con­ser­va­tion (DOC) as part of the con­ser­va­tion es­tate. With­out much hope of suc­cess I con­tacted DOC, the lo­cal iwi, Te Hapu¯ o Nga¯ ti Wheke, and the Otamahua / Quail Is­land Eco­log­i­cal Restora­tion Trust, who are all stake­hold­ers in the is­land. The DOC’s po­si­tion was that noth­ing should be taken from con­ser­va­tion land with­out per­mis­sion, un­less I had a prospect­ing li­cence. So that was that. In­ter­est­ingly King Billy Is­land is known as ‘Aua’ to the Ma¯ ori. An­other mean­ing of ‘aua’ is “I don’t know”. A sit­u­a­tion rem­i­nis­cent of the In­dige­nous Aus­tralian word ‘kangaroo’, which has the same mean­ing.

I rang the Ge­ol­ogy Depart­ment at the Uni­ver­sity of Canterbury and talked to one of the pro­fes­sors. He told me that there were are other sand­stone out­crops in the an­cient vol­cano caldera that forms Lyt­tel­ton Har­bour. Th­ese are the re­mains of the seabed that the vol­cano thrust through mil­lions of years ago. One is at nearby Or­ton Bradley Park, which is owned by a char­i­ta­ble trust. I ap­plied to the park man­ager to get a small block of the sand­stone, to which he was agree­able. On the day, we trudged through the rain and mist to the quite ex­ten­sive, well-fenced quarry which was last worked more than 40 years ago. The man­ager thought it was un­wise to ap­proach the work­ings too closely, es­pe­cially as wa­ter was run­ning down the rock face and a rock fall was not out of the ques­tion. There was plenty of sand­stone rub­ble among the gorse bushes be­low the quarry face, and he very kindly gave me a plate-sized piece. We dis­cussed whether Mr Bradley, the orig­i­nal owner, would have used the sand­stone to make grind­ing wheels such as the ones in the old sawmill on the prop­erty.

The man­ager thought that the grind­stones were prob­a­bly English, but he pointed out that one of them, pow­ered by the over­shot wa­ter wheel, had ‘1900’ carved into its side. Would you do that to a pur­chased grind­stone, or would the rough sides of the grind­stone in­di­cate that it had been made on the prop­erty with stone from their quarry?

The an­i­mal-wel­fare or­ga­ni­za­tion where my younger daugh­ter worked be­fore she went back to uni­ver­sity has a bench-top man­u­fac­tur­ing busi­ness be­hind it owned by Shane Boyd. For a small fee Shane cut the Or­ton Bradley Park stone into three pieces with the 450mm wa­ter-cooled di­a­mond blade of his Ital­ian com­puter nu­mer­i­cal con­trol (CNC) bench-top ma­chine. This pro­duced a 200x100mm sharp­en­ing area. The sur­face came up well, with a creamy colour with red-brown flecks. I used wa­ter as a lu­bri­cant, just like the Or­ton Bradley Park grind­stone, as I slowly sharp­ened a chisel that I found at an op shop to a near-mirror fin­ish. Re­sult! A big thank you goes out to Clive Fugill, Vicki Blyth, and Lisa McDon­ald from Canterbury Mu­seum, as well as the staff at the beau­ti­ful Or­ton Bradley Park for their help in the writ­ing of this ar­ti­cle.

A few of the adzes in Canterbury Mu­seum’s col­lec­tion. Some have been smoothed over their en­tire sur­face; oth­ers roughly shaped, with only the cut­ting edge ground smooth. The first Euro­peans in New Zealand de­scribe how Ma¯ ori would fill any idle mo­ments by pol­ish­ing their stone tools. This shows the high re­gard in which th­ese ob­jects were held

Be­low: An adze blade be­ing formed. (Re­pro­duced with per­mis­sion from Clive Fugill, Te Toki me te Whao: The Story and Use of Ma¯ ori Tools [Ora­tia Books, 2016])

Above: A ho¯ anga from Canterbury Mu­seum’s col­lec­tion. It has been worn to a dish shape by gen­er­a­tions of sharp­en­ing

Be­low: Dif­fer­ent-shaped oil stones

A Ja­panese wa­ter stone

Left: The piece of Or­ton Bradley Park sand­stoneAbove: The cut stoneBe­low: The ‘as found’ op-shop chisel Bot­tom: Sharp­en­ing the op shop’s Marples chisel on the Or­ton Bradley Park sand­stone whet­stone

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