I spent some time looking in internet for a good guide on how do achieve this, and I finally settled on one I liked (linked in the technical section as a reference). It took me a couple of tries to get the correct size of the general picture and the lines I wanted, but I got a sketch that I was happy with, and I inked it with a micron pen. Then I started filling the empty spaces with small shapes for the pieces of glass that would make the windows. 

Halfway through I noticed that I would need an overall frame for the image, and I panicked for a moment because I had calculated the triskele to jut just right in the space I had, but luckily the math of the triskele made a couple of millimeters smaller so I could fit an outer circle as the frame of the window. 

Making all those tiny shapes was tedious, and I was happy when I had finally inked the last of them. 

Now normally this would be the point where I would transfer the design into the pergamenta or parchment to start the final version. However I was not feeling sure about how to place the colors I wanted to use. I wanted a pride rainbow in one spiral, the colors of their barony in another one and in the moment I decided to go with the colors of the bisexual flag for the last one. I wanted both the pride and bisexual spirals to show the colors more or less in the same proportions of their flags, and I was concerned that correcting mistakes in this scroll would ruin the clean lines I wanted, so I decided to go with a full colored sketch of the image I wanted. 

I started by drawing faint lines defining what areas would go which color and after that got to color the glass pieces using brush markers for two reasons. One because they would require more time and second because I wanted to give dimension to the triskele using a central ridge that I was not sure yet how to shade. 

When it came to color the stone, I started by using gray as a base color and before I started working with the shadows, I decided to ask some people that know more than me in the subject where should I place the shadows. I had a general idea when but when I tried to hatch them with a mechanical pencil it just did not look right. I drew arrows showing the direction of the light and using their example as a guide, I colored the shadows of the stone, first lightly with a mechanical pencil and then with the same brush markers.

Happy with the results, now I faced the question on how to transfer this design into their final piece. This was by far the most detailed piece I've done so far and the watercolor paper the sketch was done on did not allow my light table to shine through enough. 

Next was the flat colors of the "mortar" and the "stone". For the mortar I mixed a very light grey from zinc white and lamp black and used one of my miniature brushes to paint it, trying to make all the edges neat and the corners as sharp as possible.

For the stone, I mixed a slightly darked grey and I also added a hint of vibrant green and ultramarine blue, to give it that blue-ish tinge that some stone buildings have. 

The last step was to paint the shades and volume of the "stone" to give the final appearance of a carving. Using the cartoon I had as reference, I did this on two steps: 

First I painted all the center of each shadow with a slightly darker grey, also with blue and green added. These were the darked parts, and the shadows would fade to the sides as they came around the ridged spirals. 

Next, I mixed a medium tone directly from the darker grey and painted the borders of the shadows on each side of the darker areas. I could have omitted this step, but this made the blending of the colors easier for me.