Make sure you have a photoresist film with a layer of adhesive. Even if you are using a self-stick photoresist film, an additional layer of adhesive should be applied for the photomask to adhere to the wood surface. A 5Mil or 6Mil photoresist film works great on wood surfaces, which allows the blaster to increase the blasting pressure. A higher pressure will speed up the blast time and obtain depth faster.
Sandcarving wood relieves the wood grain but provides no contrast. A clear coat or a color paint-fill application is recommended for the etched area. I recommend using aluminum oxide in place of silicon carbide for wood surfaces; silicon carbide is reflective and will shine through paint if it is not cleaned properly.