Which action can increase the working time of alginate?

When considering the factors that influence the working time of alginate, using colder water than room temperature is the most effective approach to increase its working time. Alginate sets through a chemical reaction with water, a process that can be accelerated by temperature. Cooler water slows down the setting reaction, giving the practitioner more time to work with the mixture before it begins to set. This is particularly useful in dental applications, where precise handling is required for molds and impressions.

Adding hotter water, on the other hand, would accelerate the setting time, resulting in a quicker solidification of the material, which is opposite to the desired effect of extending working time. Mixing with a spatula doesn't inherently affect the chemical reaction time; rather it relates to the method of incorporation of the components. Lastly, while adjusting the powder-to-water ratio can affect the consistency of alginate, it does not significantly alter the working time in the same way that temperature does. Thus, using colder water effectively prolongs the usability of alginate by slowing the reaction rate.