Table 2.

Properties of purple-sand female mold calcinated with different times (at 960°C)

Time (hours)	1	2	3	4	6	8	12
Colora	+	+	++	++	+++	+++	+++
Breathabilityb	+++	+++	++	++	+	+	+
Siphonagec	+++	+++	++	++	++	+	+
Shrinkage-1 (%)	86.8	85.5	84.8	84.1	82.3	80.9	80.6

Notes:

^a+, yellow; +++, black.

^b+++, polymer solution can be pulled into microholes within 1 minute; ++, ≤5 minutes; +, >5 minutes.

^c+++, hydrophilic and diffused; ++, hydrophilic; +, hydrophobic.