Admittedly, I did not do any crown shaped drop collision until two years after I started water drop photography even though it is relatively easy to do. A crown drop collision looks something like this and I am going to describe some steps to get this kind of collision:
This is a typical Crown collision
This type of collision is not caused by two streams of liquid, but only one stream of drops and a hard surface. Normally, in order to get some reflection, the hard surface must be reflective and smooth. A shiny glossy black acrylic board is well known among dropper community. Here is an example of it:
To get reflection, the angle of shot is also important — usually at very low angle relative to horizon. This low angle requires larger size of the acrylic board otherwise, it is very easy to shoot outside of the board. Of course, if you want to get a inside shot of the collision like below, you can use smaller piece of acrylic boards.
This is shot almost straight down and the inside of collision is revealed.
One thing about crown collision is that you can get multiple colors in one shot with only ONE valve!!! The trick is to use different colored liquid to make a small puddle where the drop will be hit upon. The result is an muti-colored crwon. Here is one example of it
In this example, only one valve dropping white colored liquid down to two colored puddle
Here is a video I made a while ago and you can see a complete crown being made in action.
So to summarize the process, here are steps to make it happen:
Step 1 — Prepare liquid. I use gum mixture solution and then add food color or acrylic paint into it. Mix it well and put it in small bottles like the one shown with black acrylic sheet above. Make more than one for different colors.
Step 2— Put a black (or white) acrylic sheet at where the crown will be.
Step 3 — Add some liquid to the bottle from above that is controlled by water drop controller. Drop a small drop (like 15ms sized drop) on to the acrylic sheet and take a shot. This has two purposes: one is to find out where the drop will be landing at so we can create a puddle around it. The other purpose is to test the angle and field of view, to see if anything is not desirable. If you move the acrylic sheet so that nothing outside of it is in the view, you need to clean the sheet and drop a small drop again to find the spot.
Step 4 — Once you are happy with the position of acrylic sheet and have located the spot where the drop will land at, add more liquid, maybe different colored ones to form a small puddle. This is very import because without this puddle of liquid, it is very hard to get a crown.
Step 5 — Repeat step 3 and 4 for different Flash Delay (FD), this will allow you to capture different stages of the crown. For example, the following is at very late stage and the collision is almost finished.