I recently did some work on my Swan bass harmonica. I realized the extra large size made everything easy to see, so I took some photographs for sharing.
Descriptions have been added for folks who know very little if anything about embossing.
Embossing involves narrowing a reed slot by rubbing a hard smooth object along the 90 degree edges of the slot opening. This is done to bend (burnish) the metal edge into the slot. A tighter fitting reed requires less air to move it. This does not necessarily make the harmonica "better" but it can make a harmonica more sensitive and air efficient.
In the case of my Swan bass I could literally hear excessive air moving past the reeds. I have played this harmonica enough to realize that I wanted to tighten the fit of the reeds and to reduce some of the gaps at the reed tips. It's a blow only harp that requires a lot of breathing.
Here's a shot of the bass harp partially dismantled. The Marine Band shows the scale. I normally use the tuning fork for embossing reed slots. It felt too small in this case so I used the wood handled "burnisher". The burnisher is a woodworker's tool used in a similar manner to put a cutting edge on a "cabinet scraper".
Here's the burnisher in action. Several passes are required along with some lubrication. The tool is held nearly flat with the surface then the angle is gradually increased with each pass.
This image shows a reed slot that has not yet been embossed. The surface of the Swan bass reed plates are pretty crude and harder than typical brass plates.
The shiny area is where the metal has been burnished downward and into the slot. It normally doesn't take much effort.
Some back lighting will reveal the reed clearance. Over embossing will cause the reed to buzz or stick.
More importantly, I adjusted the height of several reed tips before I reassembled the harmonica. This look from the back side of the reed plate shows 2 of the 5 gaps were excessive here.
The work really paid off. The Swan bass responds quicker using much less air and it's easier to produce expressive bends with this beast.
Embossing will do more harm than good for an absolute beginner but if you are an accomplished beginner you may want to try embossing. It's an easy and reversible modification.