§175.390 Zinc-silicon dioxide matrix coatings.
Zinc-silicon dioxide matrix coatings may be safely used as the food-contact surface of articles intended for use in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food, subject to the provisions of this section;
（a） The coating is applied to a metal surface, cured, and washed with water to remove soluble substances.
（b） The coatings are formulated from optional substances which include:
（1） Substances generally recognized as safe.
（2） Substances for which safe conditions of use have been prescribed in § 175.300.
（3） Substances identified in paragraph （c） of this section, subject to the limitations prescribed.
（c） The optional substances permitted are as follows:
| List of substances | Limitations |
| Ethylene glycol | As a solvent removed by water washing. |
| Iron oxide | |
| Lithium hydroxide | Removed by water washing. |
| Methyl orange | As an acid-base indicator. |
| Potassium dichromate | Removed by water washing. |
| Silica gel | |
| Sodium silicate | |
| Zinc, as particulate metal |
（d） The coating in the finished form in which it is to contact food, when extracted with the solvent or solvents characterizing the type of food, and under the conditions of its intended use as shown in table 1 and 2 of § 175.300（d） （using 20 percent alcohol as the solvent when the type of food contains approximately 20 percent alcohol） shall yield total extractives not to exceed those prescribed in § 175.300（c）（3）; lithium extractives not to exceed 0.025 milligram per square inch of surface; and chromium extractives not to exceed 0.05 microgram per square inch of surface.
（e） The coatings are used as food-contact surfaces for bulk reusable containers intended for storing, handling, and transporting food.