As a result of the share price strength of speciality chemicals supplier Elementis over the last two years, RBS downgrades its rating to 'hold', from 'buy'.The shares have risen more than sevenfold since their low in April 2009, and have jumped by 19% in the year-to-date, outperforming the STOXX 600 Chemicals index by 14%, according to RBS.The broker notes that the strong performance was as a result of solid 2010 figures and last week's first quarter update, in which the group said it expects earnings to be at the upper end of expectations.After raising its 2011-13 earnings per share forecasts by 3-5%, RBS says that it sees limited upside and believes the "current share price fully discounts what we see as further recovery potential."The target price is raised to 160p, from 155p.---bc