Paint

It is essential that interior paints used for pots, trays or walls be nontoxic and without persistent odor. Some house paint contains mercury or other substances as a fungicide and should definitely not be used inside an oven. Such paint gives off toxic fumes even at room temperatures and would give off even more at cooking temperatures. Nontoxic white paint has reportedly been used for inner sides in place of foil. It is important that the white be as shiny and white as possible. Such ovens have generally cooked less well than similar foiled models. Ceramic paints so far have not performed well and give off odor for very long periods of time as well as performing poorly.

For trays and the outsides of pots, any dark color will produce heat better than any light color. Light-colored or bright pots reflect solar radiation away and so are slower to heat, or heat only from the hot air with little or no heat produced on the surface of the pot. Dark red, dark green, dark blue, and dark brown colors may be used. Paints on pots are best kept thin since thick paints insulate. On surfaces darkened by handicraft methods even "nontoxic" paints still may not be safe for ingesting so food should not be laid directly on a home-painted tray but needs to be cooked inside a pot or on a commercially dark tray. Paints that contain toxic solvents may be used ONLY IF THE TOXIC SOLVENT WILL BE COMPLETELY DRIVEN OFF BY PREHEATING. Determine this by using only commercial paints recommended for barbecue equipment or other specific food-related uses. Nontoxic homemade paints include children’s non-toxic black paint powder, such as Tempera, soot from clean wood mixed with nontoxic water-based glue or soot mixed with cooking oil that smokes at low temperatures. High temperature cooking oils will remain sticky indefinitely but low temperature oils will become baked on.

Any new solar box cooker is best heated initially for several hours without food to clear out any residual vapors. Some engine and conventional black paints never get over releasing heavy odors and will ruin an oven. If in doubt, run a preliminary test before risking any questionable paint.

Any exterior paints or varnishes may be used to weather-proof the outside of the oven. The color of the outside does not affect oven temperatures if insulation is adequate.

[Text for this article was originally taken from The Expanding World of Solar Box Cooking by Barbara Kerr]