Question.
I am completely confused on what material to use when. I see you have the choice of wheat flour, rice flour, saw dust, tonoko, jinoko. When do you use them? Also, do you have to first apply any ‘primer lacquer to the surface of the broken ceramic before putting them back together.

Answer.

I don’t apply lacquer to the broken face before applying mugiurushi although you can. If you do you should only do it on high fire bodies as middle to low fire bodies may absorb and wick the lacquer and stain your break line.

Regarding the different materials, flour, rice, etc.
I use them with the following in mind.

Wheat flour.
I use it mainly to mix with water then basic lacquer to make a mixture called mugi-urushi, mugi = flour, urushi = lacquer in Japanese. I use mugiurushi to stick things back together, it is like a ‘glue’. It has strong tensile strength, poor compressive strength. It has strong adhesion, poor workability. That is, it doesn’t stay where you put it, it tends to bounce back out after you remove your palette knife. Because of that it makes a poor choice for filling chips and secondary filling, i.e., mismatches in the body after the initial fitting of a piece back together. It also doesn’t sand well so it isn’t good for filling chips. Its tensile strength seems to make it a good candidate for filling in restoration areas but it is so unworkable that not only won’t it stay where you put it it doesn’t sand well making it a bigger problem for doing finishing steps.
Mugiurushi also serves as a basis for mokuso which is mugiurushi plus sawdust.

Rice, flour or in a cooked state.
Rice and basic lacquer have both high tensile and compressive strength. That makes them good for sticking things back together and subsequent shaping. The best is cooked mochi rice but it takes a long time to make so I usually use rice flour. I rarely use rice because the texture after it is dry isn’t easy for me to shape. It can often chip and crumple at the edges which makes it less desirable.

Tonoko and Jinoko.
I use jinoko for filling chips. It is mixed with water and basic lacquer. It is very cooperative in the sense it stays where you put it and sands and shapes very easily. It has good compressive strength but not high tensile strength so it isn’t good for sticking pieces back together.
Tonoko is usually used for filling chips with Jinoko added when you need extra strength. Tonoko is a finer mesh material which also allows it to be used as a polishing agent for rounded metal.

Sawdust.
Sawdust added to mugiurushi is a very strong and high body mixture called mokusou. It is very fibrous so has a lot of filling power and generally won’t crack as it dries unless it is mixed with too much lacquer. That is, it is a good filling agent when you need to fill a chip or do a restoration.