以國立故宮博物院三幅掛軸探討3D技術應用於軸頭的補配作業

The Application of 3D Technology in the Replacement of Hanging Scroll's Knobs: 3 Examples from the National Palace Museum

軸頭為裝裱掛軸形式的必要配件，當書畫收藏面臨單只軸頭的欠缺問題時按過往的修護操作跡象及書面紀錄顯示可保留原配而另尋一只軸頭補配，或是拆移原配而添裝另一對新軸頭等兩種方式。為尊重文物的歷史性，「補配」是較為符合現今文物修護原則的作法。
對於單只軸頭欠缺的補配，過往修護人員在3D科技尚未發展前多在「式樣」及「同質」兩項條件間找尋與原配軸頭類似的替代品，但是這樣的作法仍然無法因應少數以多元材質製作的軸頭類型，尤其部分經特殊工藝技術作成後其軸頭外觀也會與一般俗成之式樣有所差異，例如本文〈恭繡御製萬年枝上日初長詩意〉、〈繡線四臂觀音〉、〈緙絲極樂世界〉等三件清宮掛軸所原配的玉石雕刻及琺瑯燒製之軸頭案例。經由3D技術的輔助，前述三件案例建模不論透過掃描儀器或是人工製圖生成都能在「式樣」優先的條件下得到與原配軸頭外觀相仿的3D列印模型，經由手繪仿色3D列印模型便可與原配軸頭有著對稱協調的色彩。此方式雖然不能取代傳統工藝所蘊含的人文內涵，但在暫無合適替代品可供補配時不外乎是解決軸頭欠缺問題的另一途徑。
目前3D掃描儀器在功能及操作方式上各有特長亦有部分地限制性，除了追求解析度之高低外，也從使用者的修護需求、實務條件來為琺瑯軸頭評估合適的掃瞄方式，並在與人工製圖生成的模型相較下瞭解不同建模方式的差異性。

A pair of knobs is a necessary mounting accessory for each hanging scroll. When a single knob is lost from the hanging scroll, conservators have to search for another one similar to the original. Following the fundamental ethics of conservation, this single knob replacement method is more appropriate than removing an original and attaching a new pair of knobs.
Prior to 3D technology, conservators had to choose a replacement knob based on original's style or material. However, this method was insufficient for some knobs made from multiple materials or with specific craftsmanship, such as the 3 hanging scrolls referenced in this article made from jade and cloisonnéin Qing dynasty（1644~1911）. Through the application of 3D techniques, conservators can obtain a knob which is modeled on original's style by 3D scanning or manual drafting. Regardless of the original source material, after toning, conservators could achieve a similar visual effect for the 3D modeled knob. This process is simpler and more efficient compare with the traditional craft, and it is appropriate for short-term conservation treatments.
The non-contact and precise characteristics of 3D scanning technology should provide conservators with an objective reference during the conservation process. However, current scanning instruments have their own specialties and limitations. This article also evaluates the appropriate scanning methods based on the material characteristics and conservation needs of the enamel knobs.