During the Tudor period, lead was utilized to build roofs and windows because it was easily mailable and resistive to corrosion. Farmers would mine for lead during the summer months when their crops did not need tending to in order to generate additional income. Mining during the summer months could earn an extra £5.00 which equates to £25,000 as of 2012 when accounting for inflation. Entire families often worked within the mines because 50 barrels worth of ore and soil would be extracted per day to meet the quota of what was required to be profitable. Smelting involved the use of white coal which is effectively dried wood from a kiln and was always setup upon windy hilltops or mountains because the wind would cause the fire blaze with more intensity therefore reaching higher overall temperatures. The best wood to make white coal is oak. Kilns must be airtight, so gaps were filled with clay. Knowing a kiln to be airtight was easily verifiable by searching for smoke as if smoke only came out of only the front entrance, the kiln was considered airtight. Ore was smashed into small pieces to help it smelt more rapidly which yielded approximately an 80% return upon investment. Metals were then refined using a secondary kiln, and smelted to remove any ash or impurities. The first burn removes ore from the rock, and the second burn removes impurities with the main impurity being sulphur. Molds were constructed using sand and wood to create divots which allowed the ore to be molded into blocks much the same as a modern day bar of gold. The sand gives the mold an indentation which archeologists use to identify Medieval bars of smelted ore