Early traders bound for the island of Sumatra
Native versus Imported Cobalt
Though my resource literature is on a much broader scale, most (if not all) of what I say can be confirmed in Hobson1, The Wares of the Ming Dynasty, considered by many the Bible of Chinese Porcelain. I will often give reference. My starting point is of course the year 1368, the beginning of the Ming dynasty. I've tried to arrange things in a chronological manner, but will at times break out of the period for a key reference, or note.
First a brief introduction to the two main varieties of imported cobalt.
Mohammedan Blue2 or Persian Blue, also called Hui Hui Qing or just Hui Qing. The name given to imported cobalt obtained via the overland route (Silk Road). This variety of cobalt was in use for most of the 30 year span of the Hongwu reign. It's source was different mines within Persia, India, and possibly other regions within the Arab world, as it's name implies. It's known for it's bright blue color and soft wash-tones. The presence of the trace element arsenic combined with the absence of the trace element manganese contributed to it's bright blue tone.
Sumatran Blue3 also called Su-ma-li, Su-ma-ni, Su-ni-p'o, or Hui hu da Qing. The name given to cobalt imported after the reign of Hongwu. It's source was from between the first return voyage of Zheng He in 1407 to the last return voyage in 1433, or delivered by envoys from Sumatra in the years 1426, 1430, 1433, and 1434. It's known for it's deep blue color and seemed to appeal to the tastes of the new world. Though the name (translation) may be correct, the impression it gives is not. The island of Sumatra was the trading port, not necessarily the origin of the material. The origin now offered a much wider variety as compared to what the overland route provided. And now, being somewhat more abundant, the materials were often combined.
There are two other names used to further categorize the pigment which specifically call out the reigns Yongle, Xuande, and the later reign of Jiajing (1522-1566). Though the names are rarely used, they are worth mention since they are usually incorrectly categorized as Mohammedan Blue, and not Sumatran Blue. The names are Mohammedan Bile and Lajvard Blue. The latter is sometimes called Lajivard or Lajvardi and is the Persian word for Lapis Lazuli, referring only to the color, as the stone was not used in the pigment. Still, both fall in the Sumatran Blue category, having properties of rich, dark blue, and containing black and silver specks where thickly applied.
I myself would simplify it in calling the two varieties of imported cobalt Early Mohammedan Blue for the cobalt used during late Yuan and most of the Ming Hongwu period, and Later Mohammedan Blue for the cobalt obtained from the voyages after the Hongwu reign.
Though there is little to differentiate between the two, there are subtle differences in color and tone. Some quite noticeable, and some not so noticeable. Treated as a precious commodity, these supplies were carefully measured out and inventoried. The quality of each was noted as it was first used. Any supply of inferior quality was set aside for other than Imperial use.
Keep in mind that scattered quantities of the latter, Sumatran Blue, were possibly intermixed with those from the same mines of the earlier Mohammedan Blue, adding to the confusion of differentiating between the two in the later reigns.
At the start of the Ming dynasty, emperor Hongwu reopened the Imperial kilns which had been closed for some years under the Yuan rule. Up to this time, supplies were limited to what was allowed into China via the overland route by the now defeated Mongols. The imported cobalt used at the beginning of the Ming dynasty, Hongwu period, was what was left over from the earlier Yuan stores. The overland route was mostly closed at the beginning of the reign of Hongwu. China turned inward to itself, focused internally on the building of the new Ming dynasty. Internal wars and continued Mongol threats made trade by the overland route to dangerous to consider.
Luckily the supplies at hand of the imported Mohammedan Blue cobalt were sufficient to start with, but they gradually depleted. The supply was all but exhausted nearing the end of the reign. When Hongwu died in 1398, ending the reign, the overland route was practically closed to further trade.
Little is mentioned of the brief reign of the second Ming emperor Jianwen, grandson to Hongwu. But things started to happen in 1402 when Yongle took the throne as the third Ming emperor.
With fresh supplies of cobalt no longer available, the potters now had to rely on the dwindling supplies at hand. This meant supplies previously set aside due to inferior quality of tone or color, now had to be used out of necessity. This explains the noticeable difference between the early wares of Hongwu, having a bright blue of a softer shade, as compared to the deeper shades of blue of the succeeding reign of Yongle, and especially that of Xuande.
Known for his commitment to the arts, Yongle was very concerned over this dilemma. To quickly re-establish trade and replenish the much needed supplies, he wisely initiated the seven voyages of Zheng He, sending a massive fleet of envoys to open trade by sea. The first voyage departed in 1405. Starting from the first return voyage in 1407 till the return of the last voyage in 1433, trade goods were obtained from India, the Persian Gulf, Southeast Asia, Africa, Malacca, Siam, and possibly other seaports along the routes traveled. It is noted that the cobalt was not received in large quantity, and that it may not have been present on all seven of the return voyages, making it still a rare and precious commodity. Hobson also states that it is noted in the Ming Annals that envoys from Sumatra brought supplies of Mohammedan Blue in the years 1426, 1430, 1433, and 1434. As previously mentioned, the cobalt obtained at these later periods is now referred to as Sumatran Blue, the deeper tone.
This is also defined in a later reign as Hui hu ta Qing, or deep Mohammedan blue, referring to the deep, darker blue of some Xuande wares. Though I like this term since it specifically identifies a reign, and describes the color, it also adds to the confusion by being categorized with true Mohammedan Blue of the earlier period.
In 1435, the emperor Xuande died and the reign ended. China entered a time of political unrest and instability known as the Interregnum Period (1436-1464). With the voyages now ended and the overland route closed, the supply of Mohammedan / Sumatran Blue was again cut off. What little amount remained would have been reserved for Imperial use. But closure of the Imperial kilns during this time of unrest almost guaranteed it's non-use. Not much is mentioned of porcelain manufacture during this time. It was of course continued in private kilns to meet local supply and demand.
It wasn't until the reign of Chenghua (1465-1487) that the Imperial kilns were reopened and porcelain manufacture was resumed in full swing. One problem though, there was practically no Mohammedan / Sumatran Blue available. With the resume of foreign trade, and the increased demands of the Imperial court, a new problem was at hand. Native cobalt had to be used to meet the demands. Though there was a sacrifice in the color of blue, it was offset by the exquisite wares produced during the reign. The now forced use of native cobalt revealed a very valuable property which would lead to it's continued use, and to a greater extent than before. The potters discovered that the native cobalt had less of a tendency to run during firing than the imported variety.
In 1486, nearing the end of the reign of emperor Chenghua, the precious import variety of cobalt was once again available. Now the potters experimented by mixing the two cobalts. They discovered that using a mixed ratio of 1 part native cobalt to 10 parts imported cobalt resulted in less run during firing. Different ratios were tried, but as the quantity of the native variety was increased to 2, 3, and even up to 6, the tone of the blue became too dull. Though private kilns used a cobalt mix ratio of up to 6 to 10, a ratio of no more than 1 to 10 was used for Imperial porcelain. The result was a finer detailed outline with wash-tones staying better within their boundaries. A key note here is that the once again available imported cobalt, known as Su-ma-ni, was a darker tone of blue as compared to the brighter more pale variety used for Hongwu, and late Yuan.
Being too late to affect the wares of Chenghua, the first appearance of this is of course seen in the porcelain of mid to latter period of Hongzhi (1488-1505).
Another key thing to note is that native Chinese cobalt, be it of the Bi-tang or Shi zi Qing variety, was in use, however slight the mix, from about 1436 to the present. It was the potters of the Qing dynasty, during the successful reign of emperor Kangxi (1662-1722) that perfected the refining process of the native cobalt to where it could rival Mohammedan Blue.
Perhaps I should say Confusion instead of Conclusion as I'm sure it is a bit confusing. Just keep in mind the old rule, there are always exceptions. Over the 276 year span of the Ming dynasty, many varieties of both imported and native cobalt were used resulting in many different tones and shades of blue. A piece having definite signs of age that exhibits no sign of native cobalt has a very good possibility of being early Ming, or quite possibly Yuan.
I am starting to see an increase in the use of the term su-ni-bo (or sunibo) in articles and discussions of Mohammedan Blue, the origin of which I believe to be the result of a small error I've found in Hobson's 1923 publication "The Wares of the Ming Dynasty". Just my own theory, but seeing use of the word on the rise has me concerned. Click here to view the info.
1 R. L Hobson The Wares of the Ming Dynasty 1923
2 Mohammedan Blue -also called Hui Qing or Hui Hui Qing.
3 Sumatran Blue - also called
Su-ma-li, Su-ma-ni, or Su-ni-po.
Sumali Sumani Sunipo