<prompt> In plaster of paris, the setting time is primarily altered by:Altering PL ratioAltering temperature of mixing waterSpeed and length of hand spatulationAddition of accelerators and retarders  <response>: Chemical modifiers have been used extensively to increase or decrease the setting time of gypsum products; they are called retarders and accelerators respectively. The manufacturers use both types of compounds to formulate gypsum products with specific setting times.Reference: PHILLIPS SCIENCE OF DENTAL MATERIALS, 12th ed page no 186 