This week, the ratings of four chemicals stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Airgas, Inc. (ARG) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Airgas is a distributor of industrial, medical, and specialty gases and hardgoods, such as welding equipment and supplies. To get an in-depth look at ARG, get Portfolio Grader’s complete analysis of ARG stock.

Kronos Worldwide, Inc. (KRO) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Kronos Worldwide produces titanium dioxide pigments. The stock gets F’s in Earnings Growth, Equity and Cash Flow. Margin Growth and Sales Growth also get F’s. For more information, get Portfolio Grader’s complete analysis of KRO stock.

Innospec (IOSP) earns a D this week, falling from last week’s grade of C. Innospec manufactures fuel specialties, performance chemicals, and octane additives. The stock also gets an F in Earnings Surprise. For a full analysis of IOSP stock, visit Portfolio Grader.

The rating of Tredegar Corporation (TG) slips from a C to a D. Tredegar manufactures plastic films, elastics and laminate materials, mainly for personal and household care products and packaging and surface protection applications, through its subsidiaries. The stock also gets an F in Earnings Momentum. The stock currently has a trailing PE Ratio of 41.50. For more information, get Portfolio Grader’s complete analysis of TG stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.