Here's a full-size crop of dsc35226.jpg, taken at the Cradle of Aviation, of a section of a lunar module ascent propulsion system engine. From right to left, it shows the metal casing at the forward end of the engine, then what would appear to be a thin liner between the thrust chamber and the metal casing, followed by the fiberglass filament winding of the engine bell, and finally the ablative inner lining. This crop is from the throat, where temperatures and pressures dictated a thicker ablative coating.

This engine certainly seems to have been hot-fired, probably either several times and/or for an extended duration, as most of the ablative liner has lost its terra cotta color, charred, and turned black.

Full-size crop of dsc35226.jpg.
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Picture by heroicrelics.org.

The ablator here, at the combustion chamber and throat area, is of a different material than the rest of the thrust chamber, which more resembles the apparently-fired APS engine at Glenn Research Center.

Full-size crop of dsc35230.jpg.
Click image for original version of picture; opens in a new window.
Picture by heroicrelics.org.