Formulary TD-31, Substitute For SectolL Soft(R), is a neutral-tone, low contrast print developer similar in properties to Selectol Soft. Formulary's TD-31 Sustitue For Selectol Soft® is a neutral-tone, low contrast print developer similar in properties to Selectol Soft. It produces subtly softer, cleaner prints than Selectol Soft, but the differences are very small. Use the same dilution you would for Selectol Soft. This is normally 1 part stock to 2 parts water, with a developing time of two minutes. For greater contrast, TD-31 developer can be diluted 1:1 or even used full strength. For less contrast TD-31 can be diluted 1:3 or 1:4.