Soft fired greenware is fired in the kiln to cone 018. The porcelain becomes hard enough to clean the seams and polish the parts to a smooth as glass finish. I like to soak the parts in room temperature distilled water and clean while wet to avoid breathing the porcelain dust. Once every part is smooth I let them dry for 2 - 3 days before the hard fire. The last photo shows the difference between leather hard porcelain and sfgw that has been cleaned and polished. What a difference!