After you have completed the repair on your ceramic by applying epoxy putty, sabi and kokuso, or what ever you used, a couple of base coats are needed to obtain a smoother surface and sealed before final urushi and metallic powder application. These base works are called Shita-nuri (undercoat), Naka-nuri (middle coat.)

YouTube link:
Kintsugi base urushi

You need:
Black urushi, or Red urushi
Ki-urushi
Turpentine
Isopropanol (or acetone)
 
Tool:
Brush
Spatula
Humid box
＃3000 wet and dry sanding paper or Suruga Charcoal 
Water 

Preparation:
Apply Ki-urushi using cotton swab or a brush on repaired area, then place in humid Box. (leave it for a day in the box.) You can dilute the Ki-urushi with Turpentine to reduce the time it takes to dry.
Clean excess Ki-urushi with isopropanol. 

Undercoat / Shita-nuri:
Dilute black /red urushi with turpentine, apply onto the area of repair. Place the ceramic in humid box for at least a couple of days till the urushi sets.

After it sets, using water, gently sand with＃3000 sand paper, or Suruga charcoal. You might realise that excess urushi which has spilled out onto the glaze comes off by sanding.
 
The surface of black/red urushi will become matt. If there are pin holes, you need to fill it with sabi and wait till the sabi sets before applying the middle coat.

Middle coat / Naka-Nuri
Repeat the application and sanding over undercoat to create a second layer.
 
If you still find shiny spot, it is recommended to repeat the process once more if you want to achieve a smooth surface. The shiny spot means that the surface is not flat.
 
If you are happy or not a fussy person, move on to “Applying urushi and Metallic powder”.