My etch starts with the prep for heat treat , I try to make sure I have the blade cleaned up so that after heat treat I don't have any heavy clean up to do. My clay is std furnace cement that I thin with water , this lets you control the thickness of the coating and helps to get good contact with the blade. Once the clay is set I take a clay wash , the type you use for anti scale , and with a cheap paint brush the type your kids use at school.clay the edge of your hamon line. The last item I read here on the forum but can't remember who. Then I heat treat and temper keeping the temper short 1 hour or less since you have already differently heat treated the blade for a soft spine , hamons do not like heat. Now I hand sand to 2000 grit and I'm ready to etch.
My etching process I read on the forum as well , I use ferric chloride ( 50/50 with distilled water) and do short 10 sec dips and rub with a makeup cad between dips , three or four dips and you should see the back line(hamon) showing. At this point I clean the blade with windex to nutralis the ferric chloride then clean the blade in soap and water and dry well.
Now I am ready to polish the blade , keep your makeup pads handy , I make a thin past of Aluminum Silicate (I am lucky I have a manufacturer near me)and 3 in one oil , using your makeup pads I polish until I have what I want , if the hamon is not as strong as I want I repeat the etching steps until I have what I want .
I still have some trial and error as we all do.
The Aluminum Silicate my daughter got for me when she worked there , a quart jar 5 years past , the largest crystal is 1 micron.