: Celf

Rydym yn parhau i nodi blwyddyn ryngwladol tabl cyfnodol yr elfennau cemegol ac, ar gyfer mis Ebrill, rydym wedi dewis calsiwm. Mae’r rhan fwyaf o bobl yn gwybod am galsiwm fel yr elfen sylfaenol er mwyn ffurfio esgyrn neu mewn calchfaen ond mae iddo lu o ddibenion eraill ac mae i'w gael ar wely'r môr ac mewn bywyd morol ddoe a heddiw.

Elfen fetelig o liw golau yw calsiwm (Ca) ac 20 yw ei rhif atomig. Mae’n hanfodol ar gyfer bywyd heddiw ac mae’n aml yn chwarae rhan bwysig yn cynnal planhigion ac anifeiliaid. Dim ond pedair elfen arall sy'n fwy cyffredin na chalsiwm yng nghramen y ddaear ac mae’n rhan o lawer o greigiau a mwynau fel calchfaen, aragonit, gypswm, dolomit, marmor a sialc.

Aragonit a calsit yw’r ddwy ffurf grisialog fwyaf cyffredin ar galsiwm carbonad ac fe gyfrannodd y ddwy at ffurfio’r ddwy filiwn o gregyn yn ein casgliad o folysgiaid. Craidd y casgliad hwn yw casgliad Melvill-Tomlin a gyfrannwyd i’r amgueddfa yn y 1950au. Dyma gasgliad rhyngwladol sy’n cynnwys llawer o sbesimenau prin, prydferth sy’n bwysig o safbwynt gwyddonol ac a ddefnyddir gan wyddonwyr o bedwar ban byd ar gyfer eu hymchwil. Caiff perlau, sydd hefyd wedi’u gwneud o aragonit a calsit, eu cynhyrchu gan gregyn deufalf fel wystrys, cregyn gleision dŵr croyw a hyd yn oed gregyn bylchog mawr. Ym myd natur, caiff perlau eu ffurfio wrth i’r molysgiaid ymateb i barasit ymwthiol neu ronyn o raean. Mae’r fantell o gwmpas corff meddal yr anifail yn gollwng calsiwm carbonad a conchiolin sy’n amgylchynu’r peth estron ac yn dynwared ei siâp ac felly nid yw pob un yn hollol grwn. Yn y diwydiant perlau, caiff pelenni bach iawn o gragen eu 'plannu’ yn yr wystrysen neu’r gragen las er mwyn sicrhau bod y berl a ffurfir yn hollol grwn.

Cyrff meddal sydd gan folysgiaid ac maent yn creu cregyn i fod yn darianau amddiffynnol iddynt. Mae hyn yn wir am anifeiliaid di-asgwrn-cefn eraill hefyd, yn enwedig yn y môr. Mae riffiau cwrel a thiwbiau rhai mwydod gwrychog (Serpulidae, Spirorbinae) yn dibynnu ar natur atgyfnerthol calsiwm carbonad i gynnal a gwarchod eu cyrff meddal. Mae gan gramenogion fel crancod a chimychiaid sgerbwd allanol caled sy’n cael ei atgyfnerthu â chalsiwm carbonad a chalsiwm ffosffad. O gastrolithau y daw’r calsiwm y mae ar gimychiaid, cimychiaid coch, cimychiaid afon a rhai crancod tir ei angen ar ôl bwrw’u cragen. (Weithiau, gelwir gastrolithau’n gerrig stumog neu'n llygaid crancod). Maent i’w cael ar y naill ochr a’r llall i’r stumog ac maent yn darparu calsiwm ar gyfer rhannau hanfodol o’r cwtigl fel darnau’r geg a’r coesau. Yng nghasgliad yr Amgueddfa, mae bron 750,000 o anifeiliad morol di-asgwrn-cefn, yn cynnwys cramenogion, cwrelau a mwydod gwrychog.

O fwynau calsiwm y gwnaed llawer o’r 700,000 o ffosilau sydd yng nghasgliadau’r Amgueddfa hefyd. Defnyddir dau brif fath o galsiwm carbonad i wneud cregyn a sgerbydau allanol anifeiliaid di-asgwrn-cefn, ac maent yn fwy tebygol o gael eu hanfarwoli fel ffosilau os defnyddir un ohonynt yn hytrach na’r llall. Mae aragonit, sydd yng nghregyn molysgiaid fel amonitau, gastropodau a chregyn deuglawr, yn ansefydlog ac nid yw’n para am filiynau o flynyddoedd gan amlaf. Wrth ffosileiddio, mae cregyn aragonit naill ai’n ymdoddi’n llwyr, neu mae’r aragonit yn ailgrisialu i ffurfio calsit. Defnyddiwyd calsit i wneud cregyn a sgerbydau grwpiau o gwrelau sydd wedi peidio â bod erbyn hyn, braciopodau cymalog, bryosoaid, ecinodermiaid a’r rhan fwyaf o drilobitau. Mae’n llawer mwy sefydlog nag aragonit ac felly mae darnau caled gwreiddiol o’r creaduriaid yn ymddangos fel ffosilau, filiynau o flynyddoedd ar ôl iddynt suddo i wely’r môr. Yn aml, gwelir grisialau mawr o galsit yn llenwi mannau gwag mewn ffosilau, fel y siambrau y tu mewn i gregyn amonitau. Mae fertebratau’n defnyddio mwyn calsiwm gwahanol i wneud esgyrn a dannedd: apatit (calsiwm ffosffad), a all bara am filiynau o flynyddoedd i wneud ffosilau eiconig fel sgerbydau deinosoriaid ac ysgithrau mamothiaid.

Yng nghasgliadau’r Amgueddfa o greigiau, mae llawer o galchfeini, creigiau a ffurfiwyd ar waelod y môr amser maith yn ôl o ddarnau o gregyn a deunydd arall sy’n cynnwys llawer o galsiwm carbonad. Ers miloedd o flynyddoedd, bu pobl yn defnyddio calchfeini i adeiladu: cerrig cerfiedig yn nhemlau eiconig y Groegiaid a’r Rhufeiniaid; darnau mâl i fod yn falast o dan reilffyrdd a ffyrdd; neu wedi’u llosgi i greu calch i wneud sment. Defnyddiwyd calchfaen enwog o Dorset o’r enw Carreg Portland i adeiladu Amgueddfa Genedlaethol Caerdydd ac adeiladau eiconig eraill yng Nghanolfan Ddinesig Caerdydd. Ar lawr yr Amgueddfa gwelir teils marmor, sef calchfaen a drawsnewidiwyd o dan wres a gwasgedd mawr. Bu cerflunwyr yn hoff iawn o farmor ers dyddiau’r hen Roegiaid a’r Rhufeiniaid. Yng nghasgliadau celf yr Amgueddfa gwelir gweithiau marmor gan Auguste Rodin, John Gibson, Syr Francis Chantrey, Syr William Goscombe John a llawer o rai eraill. Yn ogystal, mae yno enghreifftiau pwysig o waith gan gerflunwyr o’r ugeinfed ganrif, fel Jacob Epstein, Eric Gill a Henri Gaudier-Breszka. Roedd yn well ganddyn nhw gerfio calchfaen feddalach a llai dwys, Carreg Portland a thywodfaen.

Many of the books in the Library collections at the National Museum Wales have attractive decorative techniques applied to the covers or text blocks. Decoration on text blocks, the combined pages of the book inside the covers, is particularly lovely because it tends to be hidden when they are on the shelves.

The most popular examples of decorating text blocks include marbling and gilding. But one of the most interesting techniques is the one known as disappearing fore-edge painting, which was often hidden underneath the other types of decoration.

Fore-edge painting was a technique that reached the height of its popularity from the mid-17th century onwards. It was usually applied to the longest section of the text block, the one opposite the spine, the fore-edge.

Two books in our special collections feature examples of mid-19th century disappearing fore-edge paintings. They are the two volumes of the second edition of the Memoirs of Lord Bolingbroke by George Wingrove Cooke, and were published in 1836.

When the book is closed you cannot see the image, only the gilt edges of the text block, but when the leaves are fanned, the hidden picture is revealed.

To achieve this effect, the artist would need to fan the pages, and then secure them in a vice, this means they are applying the paint not to the edge of the page, but to just shy of the edge. Once completed, it is released from the vice and the gilding would be applied to the edges.

Landscape scenes were the most popular for this technique, and the ones on our books show Conway Castle and Caernarfon Castle.

Very often the motivation for a fore-edge painting was a demonstration of artistic skill, so it didn’t always follow that the images were related to the text contained within the book. These two volumes of Memoirs, do not have an obvious connection to the scenes painted. Lord Bolingbroke (Henry St John, 1st Viscount Bolingbroke 1678–1751) was an English politician during the reign of Queen Anne, and later George I, and is probably best known as a supporter of the Jacobite rebellion of 1715, but he does not appear to have any direct association with either Conwy or Caernarfon.

The volumes were acquired for the Library in 2008 from a rare book dealer, but we don’t know enough about their history to be able to tell when the fore-edge paintings were added. The first volume contains an inscription that states that the book was a gift to a T. M. Townley from his friend Samuel Thomas Abbot on his leaving Eton in 1843. Unfortunately we don’t know anything about either the recipient or the sender, so we can’t tell if one of them was ultimately responsible for painting the books.

This St David’s Day, Friday 1 March, the Honourable Society of the Cymmrodorion will present a unique eighteenth-century painting, Poor Taff, to the museum. The Honourable Society of the Cymmrodorion has kindly offered Poor Taff to Amgueddfa Cymru and the people of Wales, following the closure of its former home, the Welsh Girls’ School (later St. David’s School) founded by the Society in the eighteenth century.

This is one of four oil paintings, possibly commissioned by Welsh Societies, telling the tale of the Welsh satirical character, Shon-Ap-Morgan, who was widely known as “Poor Taff”, and his journey to London. Shon was intent on avenging the  “rabble” English who entertained themselves by annually hanging ragged effigies of Welsh people above the streets on St David’s Day. Things did not go as planned for Shon, many versions of the story claim that the “demon drink” was responsible for his many misadventures.

He is portrayed in the painting with his attributes that include the goat he rides, leeks, cheese and herring. Some versions show him with his wife, Unnafred [Winifred] Shon. This caricature probably stems from a combination of early anti-Welsh prints and a popular Meissen figurine that originally poked fun at the tailor of the Saxony factory’s director, Count Brühl. The figurine shows the tailor riding a goat with a female companion. English factories were quick to copy this popular design that became known as “the Welsh tailor and his wife”.

This image of Poor Taff shows that he self-styled himself as a gentleman. However, he was so poverty-stricken he had to ride a goat rather than a horse. Whereas today, his diet of leeks, cheese and fish seem a healthy choice, they were seen then as further symbols of his poverty. These satirical anti-Welsh symbols were promoted in London’s popular print culture that was convenient for anti-Welsh sentiments. Some English artists used this satire on prominent public figures such as Watkin Williams Wynn and the Prince of Wales (later George IV).

Later versions of the prints however, began to praise Wales and Welsh people, condemning the previous English abuse. As a result, Shon-Ap-Morgan, or Poor Taff, became an affectionate symbol of Welsh national identity. For this reason the painting may have been commissioned by a London-based Welsh society. The stereotype that we see in this painting eventually gave way to a more benevolent Welsh icon created by Augusta Hall (Lady Llanofer) of the Welsh lady, “Blodwen”, with her tall black hat and shawl.

I gydnabod hyn, bydd Amgueddfa Cymru yn cynnal cyfres o flogiau misol, pob un yn trafod gwahanol elfen gemegol a’i harwyddocâd i Gymru. Cadwch lygad yn agored am y rhain trwy gydol y flwyddyn ar ein gwefan.

I ddechrau ein cyfres o flogiau, ym mis Ionawr rydym yn trafod arian.

Mae arian (symbol cemegol – Ag), rhif atomig 47, yn un o saith metel gwreiddiol alcemi a châi ei gynrychioli gan symbol y lleuad ar gynnydd. Mae arian yn fetel gwerthfawr ond ni fu erioed mor werthfawr ag aur.

Mae arian wedi chwarae rhan bwysig yn hanes Cymru ond nid yw hyn yn cael llawer o sylw. Yn rhan fwyaf gogleddol Ceredigion, ger pentref Goginan, mae nifer o hen fwyngloddiau a fu ymhlith cynhyrchwyr arian mwyaf toreithiog Ynysoedd Prydain. Mae bron yn sicr bod y Rhufeiniaid wedi darganfod y gwythiennau o fwynau llawn metelau yn y ddaear, ond y Frenhines Elisabeth I oedd yn gyfrifol am eu datblygu fel mwyngloddiau arian.

Dywed rhai mai Thomas Smythe, Prif Swyddog Tollau Porthladd Llundain a ddarganfu’r swm sylweddol cyntaf o arian ym mwynglawdd Cwmsymlog ym 1583. Mae’n llawer mwy tebygol mai Ulrich Frosse, peiriannydd mwyngloddio o’r Almaen a wnaeth y darganfyddiad a rhoi gwybod i Smythe. Roedd ganddo ef brofiad o gloddio am arian ac ymwelodd â’r mwynglawdd tua'r un pryd â Smythe. Yn ystod teyrnasiad Elisabeth I, amcangyfrifir bod pedair tunnell o arian wedi’i gloddio o fwyngloddiau Ceredigion.

Gwnaeth y Brenin J I a’r Brenin Siarl I elw sylweddol o’r mwyngloddiau (cynhyrchwyd 7 tunnell yn nheyrnasiad y naill a 100 tunnell yn nheyrnasiad y llall). Yn wir, ym 1638, penderfynodd Siarl I sefydlu bathdy yng Nghastell Aberystwyth gerllaw. Oherwydd ei lwyddiant, cafodd ei ddinistrio gan Oliver Cromwell a’r Seneddwyr yn ystod Rhyfel Cartref Lloegr ym 1646.

Mae gan Amgueddfa Cymru enghreifftiau o’r llu o ddarnau arian bath wedi’u gwneud o arian a fathwyd yn Aberystwyth. Un peth sy’n nodweddiadol ohonynt yw’r tair pluen ar y naill ochr a’r llall. Mae nod y llyfr bychan agored ar y darnau’n dangos mai Thomas Bushell a gafodd yr arian o fwyngloddiau Ceredigion a ran y Company of Mines Royal.

Mae'r mapiau a'r planiau a gynhyrchwyd i farchnata'r mwyngloddiau arian i fuddsoddwyr ymhlith y rhai cynharaf i'w cynhyrchu ym Mhrydain. Yn Llyfrgell Amgueddfa Cymru, mae sawl fersiwn o fapiau William Waller a gynhyrchwyd ar gyfer y Company of Mine Adventurers ym 1693 a 1704 ynghyd â Fodinae Regales Syr John Pettus a gyhoeddwyd ym 1670.

Cafodd un o’r mwyngloddiau, Bwlch yr Esgair Hir, ei frolio fel Potosi Cymru a defnyddiwyd peth o’r arian a gloddiwyd yno i wneud jwg ddŵr ac arni'r arysgrif ‘The Mines of Bwlch-yr-Eskir-hir’, tua 1692. Fodd bynnag, methiant oedd y mwynglawdd. Ni chynhyrchwyd cymaint o arian â’r disgwyl erioed ond problem ddaearegol oedd hyn yn hytrach na diffyg yn y dulliau cloddio. Efallai bod y safle’n fwyaf adnabyddus am ei ran mewn achos cyfreithiol yn erbyn rheolaeth y Goron dros fetelau gwerthfawr. Dygwyd yr achos gan y tirfeddiannwr Syr Carbery Pryse yn 1693 a rhoddodd derfyn ar ormes y Mines Royal.

Parhawyd i fwyngloddio arian mewn modd cynhyrchiol yng ngogledd Ceredigion, yn gyntaf o dan y Company of Mine Adventurers ac yna, trwy gydol y Chwyldro Diwydiannol, gan nifer o gwmnïau preifat. Cynhyrchwyd cyfanswm o dros 150 tunnell o fetel arian yn y rhan hon o Gymru.

Yn rhyfedd iawn, cymerodd tan y 1980au i ddaearegwyr adnabod y mwyn sy’n gyfrifol am fod cymaint o arian yr y rhan fechan hon o Gymru. Ei enw yw tetrahedrit – mwyn yn cynnwys copr, sinc, haearn ac antimoni sylffid – ac mae arian yn gallu cymryd lle peth o’r copr, y sinc a’r haearn sydd ynddo. Cofnodwyd bod hyd at 18%, yn ôl pwysau, o’r tetrahedrit o fwynglawdd Esgair Hir yn arian. Mae sbesimenau pwysig o fwynau a ddefnyddiwyd i adnabod y tetrahedrit yn cael eu cadw yn ein casgliadau daearegol yn yr Amgueddfa.

Nid oes metel arian naturiol yn weladwy yn yr un o fwyngloddiau Cymru ond mae rhai o’r enghreifftiau gorau yn y byd gan yr Amgueddfa yn ei chasgliad o fwynau. Mae’r sbesimenau, o fwynglawdd Kongsberg yn Norwy, o ansawdd eithriadol a chawsant eu caffael yn yr 1980au fel rhan o gasgliad R. J. King.

Hi, I’m Thea, a sixth form student from Shropshire who decided to create this short video as part of my work experience at the National Museum Cardiff.

I had heard about Who Decides? before I became involved in the exhibition, so I was very eager to find out more. After working with the public opinion cards, speaking to the people involved in the museum and doing some short interviews, I created an animation that I thought would best reflect the aims of exhibition and the feedback it had received.

I am passionate about art and against the idea that art and museums are ‘elitist’ or should be for the ‘privileged’ rather than the majority, so I wanted to focus on this issue in the video.

Working with the Wallich

The exhibition itself was incredibly eye opening for me; the museum had decided to work with the charity The Wallich to involve people with experience of homlessness in the process of designing and creating the exhibit and gives the public the chance to choose some of the artwork on display. I haven't seen an exhibition that has ever taken this kind of approach, so I found it intriguing to see how others reacted to the idea.

I hope this refreshing approach to curation will be an archetype for future exhibits and museums because it challenges what we usually connote with galleries and exhibits and hopefully encourages more people to visit exhibitions and museums.

Who Decides? is on show at National Museum Cardiff until 2 September 2018. You can also contribute to Who Decides? by voting for your favourite work to be ‘released’ from the store and placed on public display.