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景德镇传统制瓷工艺 THE TRADITIONAL CRAFTS OF PORCELAIN MAKING IN JINGDEZHEN

 

  • 利坯工艺

  • Fine Trimming

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泥坯也称“修坯”或“旋坯”,是陶瓷成型中极为重要的工序之一,使器物表面光洁、形体连贯、规整一致,是最后确定器物形状的关键环节。内外修坯是景德镇制瓷工艺中一项极为重要并优于其它窑系的成型技术,是形成景德镇陶瓷风格的一个独特的技术保障。利坯工不仅需要熟悉泥料性能,而且要熟练掌握造型的曲线变化和烧成时各部位的收缩比,以及各部分留泥的厚薄程度。一般来说,在同一器物的不同部位,坯体厚度各不相同。因为不同部位在高温烧成时的收缩率和受力情况不一致,因而利坯时应控制不同部位的泥坯厚度,以防止烧造变形。此外,利坯工还须根据不同样式的造型锉制利坯工具,校正刀具的弧度、角度,配制陶车上的利头(也称利脑、坯座)。利头的大小集合式程度直接影响到利坯的好坏和功效,故所有利坯学徒第一步需学磨制利坯刀具,第二步就是根据坯件的大小和形状来修整不同的利头,否则难以达到利坯的质量要求。利坯时陶车运转速度慢于拉坯,大部分刀具的刀口均有明显的齿纹,是锉制刀具时有意留下的,其目的在于增加刀口的锋利程度,以提高利坯功效。利坯刀具均为铁质,在锉制时首先将其放入炉火内烧红,随即取出置于水中急冷,即淬火,然后再锉制。采用淬火工艺的目的,是为了提高利坯刀具的强度和硬度,并增强其抗蚀性,以使刀具在利坯时不易磨损,也可减少刀具锈蚀而将铁锈带入坯内。如果刀具在使用一段时间后因磨损而使刀口变钝,则需将刀具按上述过程重新淬火锉制,以使刀口经常保持锋利。磨制利坯刀具时学坯工的第一道程序,在磨制刀具时,首先要将刀口磨平,使刀具保持刀口平直,利于修直瓶,尤其是板刀;然后再锉磨刀的内面刀口,最后定口时用力留下锉齿痕。通常每个利坯工所用的道具不下十余种,每种均有大小之分。

利坯时对于坯体厚薄程度的控制及其识别方法,是掌握利坯技术和确保利坯质量的关键所在,这需要依靠技术熟练程度和实践经验来掌握。利坯的作用除要做到外形美观外,也是为了尽可能减轻瓷器的重量,使作品更显精致,同时也减少原料和烧成时燃料的损耗,但过薄的型体易产生变形,故在修坯时应注意不同造型和不同部位的蓄泥情况。蓄泥不当,易导致制品烧成时沉底、凸肚、软塌等变形状态。按一般经验,测定坯体厚薄需用手指上下抚摸并轻轻弹叩,以听其不同部位的响声。为此,利坯时应及时倒出多余的泥屑,随时用手指弹听其声响。坯体较厚者,弹之发出“咯咯”带硬之声;修之中等厚度时,弹之发出“咚咚”之声;高档瓷坯体修至适当薄度时,弹之则发出“卟卟”的脆声。

薄胎器利坯时,除上述方法外,最后还可采取用毛笔滴水,由口沿直线流下以观水痕。滴水后,坯体受水浸湿,明显地留下一条湿的痕迹,如果修制厚薄不一致则坯体水迹均匀,否则坯体水迹明暗深浅不同,表明坯体不符合要求,需要再进行精细加工。

在利坯之前,坯体的厚度远比成品厚度为大,因此必须为利坯预留充分的余地。

   
 

The skills of fine trimming is also called “trimming” or biscuit throwing. It is one of the most important working processes in porcelain shaping. It is a key link both to make the final of the ware and to smoothen the surface of the ware. Its form should be coherent. The trimming of the inner and outer surface is one of the most important part of the skills of porcelain making in Jingdezhen which has much better shaping skills than other kilns. It is a technological guarantee to establish the Jingdezhen style of porcelain with distinctive characteristics. Potters for trimming are not only required to have a good knowledge of the qualities of clay and the thickness of biscuit in different parts, but also quite experienced with changes of lines in from and the degree of shrinkage of every part when firing. Generally speaking, different parts of the same ware have different thickness because each part of the ware has its own degree of shrinkage and endurance in high-temperature firing. As a result, potters should have a good command of different degree of thickness in different parts when making fine trimming in order to prevent the ware from being distorted when firing. In addition, trimming potters are also required to file trimming knives and tools in accordance with different shapes and forms and adjust the radian and angle of knives and tools. They should also learn to prepare the biscuit bats (locally called litou or linao). The size and appropriateness of the biscuit bats are directly linked with the quality of trimming. Therefore, the first lesson for all of the apprentices engaged in the trimming is to learn to file the trimming tools and the next step is to prepare various types of biscuit bats based upon the sizes and forms of biscuits. If not so, they cannot meet the requirements concerning the trimming quality. The speed for trimming on the potter’s wheel should slower than that of throwing. Most of the blades of the trimming tools have distinctive picot edge which is filed on purpose. The very purpose is to make the blades sharper so that the blade will not slip and will better the trimming. The trimming tools are usually made of iron. Before filing, first of all, put the tool in a stove. When it turns red, take it out quickly and put it into the water for a quick cooling, i.e. quenching, before filing again. The purpose of quenching is to improve the strength and hardness of the trimming tool and its corrosion stability. As a result, the trimming knife will not be worn and blend less rust with the biscuit due to the corrosion of the tools. After a period of time, the tools should be quenched and filed once again to make them sharp when they become blunt. It is the first lesson for trimming apprentices to learn to file the trimming tools. When filing the trimming tools, first, sharpen the tool edge to make it flat and straight, which is favorable for trimming vases. After this, file the inner edge of the tools and, finally, try hard to file picots over the tool edge. Trimmers usually use more than a dozen of tools and knives. Each has its large and small types at the same time.

When engaged in the fine trimming, the way to control and distinguish the thickness of the biscuit is very important in application of the trimming skills and guarantee of the quality of biscuit trimming. All of these depend upon the skills and practical experiences. In addition to bettering the outer appearances of the wares, it will reduce loss of fuels while firing and the amount of raw materials. However, too thin biscuits are inclined to become distorted so that more attention should be paid to the clay accumulation for different parts and different forms. If the clay accumulation is not appropriate, such distortions as convex bottom and soft breakdown will take place when the wares are fired. According to the common knowledge, the method to measure the thickness of the biscuit is to feel it up and down with fingers and pat it gently in order to distinguish the different sound of different sections. Therefore, it is necessary to clear out the excess clay spares out of the biscuit and listen to its sound time and again. If the biscuit is thick, a rough “gege” sound will be heard and the “dongdong” sound comes from the middle thickness. When the high-grade porcelain is trimmed to an appropriate thickness, there comes a clear and melodious sound of “ pupu” . When trimming the egg-shell porcelain ,in addition to the above-mentioned method , another method is to dip water on the porcelain with a painting brush for the last stage. We should have a close observation as the water flows straight down the biscuit . At this time when the water dips , the biscuit become wet and have a distinctive wet mark on its surface . If the biscuit is trimmed evenly ,then, the water mark on the surface is well-distributed , or it will have different shades, which means that the biscuit has not met the standards and need to be trimmed again .

before trimming , the thickness of the biscuit is much more than that of finished wares as we have had a thicker biscuit for fine trimming.

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 SHAPING 成型工艺

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