THE proposed listing of Interform Ceramics Technology has been overshadowed by a series of allegations of undisclosed joint ventures in China. Documents sent to the Stock Exchange of Hong Kong allege Interform is involved in two ceramics joint ventures on the mainland which are not listed in its prospectus. But the company has strenuously denied the claims and has taken out newspaper advertisements describing the allegations as ''groundless''. The company's $183 million share offering was launched last Thursday and is due to close on Tuesday. Sunday Money has received documents on two joint ventures allegedly owned by Interform International Ltd, the wholly owned subsidiary of Interform Ceramics, which are not shown on Interform's listing prospectus. According to Interform chairman Matthew M. P. Ngan, both joint venture contracts were cancelled ''a long time ago''. ''The allegations are totally groundless. We have disclosed all the joint ventures undertaken by the company or the subsidiaries under the company on the prospectus,'' said Mr Ngan. He said the company had signed the joint venture agreements in 1992 and cancelled them soon after. The company was not legally obliged to disclose the two projects in the prospectus and had explained the case to the stock exchange, he added. The two joint ventures are Zibo Huakun Building Ceramics Co Ltd and Anyang Dafang Ceramics Co Ltd, which are located in Zibo City, Shandong province, and Henan province respectively. According to a document received by Sunday Money , mainland authorities, including the Foreign and Trade Committee of Zibo City, certified the existence of the Zibo Huakun joint venture last Thursday, April 28. It was stated that the total investment was US$5 million, of which Interform was said to account for 30 per cent. In addition, the statement, signed by the committee, provided detailed information on the Zibo Huakun joint venture, including annual production of ceramic tiles, and certified it was still operating. A letter addressed to the Stock Exchange of Hong Kong from the China Ceramics Industry Association, which represents the major ceramics producers on the mainland, confirmed the joint venture in Zibo. The letter is dated April 29, 1994. The other joint venture in Henan, in which Interform allegedly has a 25 per cent stake with total investment of US$720 million, was certified valid on April 29 1994 by the Henan Industrial and Commerce Bureau. Herbert Hui Ho-ming, head of the listing division of the stock exchange, said that the exchange had communicated with the sponsor, Standard Chartered Asia, in regard to this matter. ''The exchange has asked them to confirm whether the information is correct or not and we are still waiting for their answers,'' he said. A Standard Chartered spokeswoman confirmed that Interform's listing would proceed. Interform supplies and installs production lines for ceramics manufacturers in China and distributes ceramic tiles, granite and marble products. According to the prospectus, the company has entered six joint ventures to manufacture and sell ceramics products in China. Its level of interest in the ventures ranges from 10 to 60 per cent. Two joint venture plants in Foshan are in operation, with a third to start operating in the city in May. Other ventures are located in Shenzhen, Beijing and Zhengzhou. As of March 31 this year, it has made a total capital contribution of about US$6.2 million to the joint ventures. Total investment from Interform and its Chinese partners is estimated at US$56 million. Since the launch of Interform's public offering last Thursday, local newspapers have received several documents on Interform's joint-venture projects in China. The company has forecast a profit of no less than HK$80 million for the year ended March 31, 1994. For the year ended March 31, 1993, Interform reported a profit of HK$36.2 million and turnover of HK$785.3 million. Interform will issue 150 million new shares at HK$1.22 each, which are scheduled to list on the local stock exchange on May 12.