He dissolved the bitumen in lavender oil , a solvent often used in varnishes , and coated the sheet of pewter with this light capturing mixture , he placed the sheet inside a camera obscura to capture the picture , and eight hours later removed it and washed it with lavender oil to remove the unexposed bitumen .
American public schools are rigidly secular . Private schools are expensive . For parents who want their children to grow up relatively unexposed to doubt , darwin or indecent lunchroom chatter , home-schooling offers hope .