I like to do as much prefinishing as I can. Its much easier to apply finish with the parts laid out on a table. Staining wood is always tricky but making a light wood (such as ash in this case) BLACK can be down right hard. The base needs to look black even in direct sunlight and not fade over time. I like to use a three part process. First I use a black dye, dye is really good at coloring face grain but doesn't quite do the job in open pores like those found in ash. I follow up the dye with a full bodied black stain. Stain is great at coloring grain and pores. These two usually are enough to get things pretty black but often the appearance in sunlight leaves a little to be desired. Lastly I apply a brushed on coat of black india ink. The result is a deep rich black that has an in-the-wood look that I think looks great!
In the middle of the three part ebonizing process
The ebonizing process leaves an in-the-wood look that doesn't obscure the wood grain
Lastly we need to do something to make sure the coloring doesn't fade over time and make it durable since people will tend to rest their feet on the trestle base. I like to use a floor finish in this case. OSMO Polyx Oil is a great floor finish that is extremely tough once cured and it also possesses UV inhibitors to prevent color fading over time. I apply OSMO with a white synthetic abrasive pad, I usually just wipe it on thick then rag off the excess, three coats like this and the base is left with a durable, beautiful and most importantly repairable finish.