The process of sculpting Maa Durga's idol is far more complex than just moulding the clay on the bamboo structure. One of the most interesting customs associated with this festival is the collection of a small quantity of soil from the doorway of a prostitute's house. This ritual has to do with concepts of purity, inclusion, and transformation.
The soil used for making Maa Durga's idol is obtained from the threshold of the home of a prostitute as per the tradition of Durga Puja. It is believed that when one goes into such a house, he/she leaves all his/her virtue outside the threshold. Hence, the soil has its own significance in the ceremony.
The culture revolves around the notion that when one enters the house of a sex worker, he/she leaves behind all the virtue and purity that he/she might have. Consequently, it is believed that the earth outside the entrance retains all this virtue and purity. That is why the soil becomes important and is regarded as one of the elements of Maa Durga's idol.
It makes for an intriguing paradox. Something that society considers unclean now transforms into a medium that produces that which is considered sacred by the ritual itself. The act represents the bringing together of what is considered peripheral in the creation of the goddess who is considered divine.
According to tradition, the sex workers sell soil from their doorsteps to the potters before Puja takes place. This soil is also sold in Dashakarma shops, where ritual objects used by the priest and artisans are bought.
The soil alone cannot be used. This soil goes into making a mixture that will form the idol of Maa Durga. In Kumortuli, in Kolkata, the soil used for making clay comes mostly from the banks of the River Ganga. As per requirement and availability, various soils can be mixed to make the clay.