This "How-To" booklet is based on specifications developed in industry committee sessions for the purpose of recommending standard specifications for use in investment castings. Topics covered include ash content; flow test; determination of softening point; determination of consistency - needle penetration method; determination of filler content - gravimetric; determination of percentage of acid insolubles in soluble wax; specific gravity of waxes and plastics; determination of filler content - by content; sink test; and dimensional stability. 2023 Investment Casting Institute.