This is a timely thread for me. I'm finishing a GSM-1 at the moment. My first attempt was with Feast Watson Prooftint in mahogany with a black burst. This was after applying Ebony Timbermate, but no sanding sealer.

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The timber took up the stain very unevenly, and it didn't look good, as much as I tried to like it. So I sanded it back, and this time applied sanding sealer before the stain. It's not exactly like for like, as I've decided to go with a natural black burst rather than mahogany. Here it is after the sealer was applied and sanded back.

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And here it is after the black burst.

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The sealer went on easily, and sanded back to a very smooth finish. It made applying the stain much easier and more consistent.