My son is obsessed with Thomas, so for his 2nd birthday, we decided to attempt a homemade Thomas the Train birthday cake for him.
I enlarged a Thomas coloring sheet & then did a trial run on a large sheet of paper. As suggested by another contributor, I traced the Thomas design onto parchment paper, then flipped the paper over and outlined it with white piping gel. Then I flipped the parchment paper onto the large sheet of paper and pressed the gel onto the paper.
I tested a variety of gels and types of frosting on the test design. I didn't like the way the gels looked alone. I used store-bought frosting tubes. Some of them were too dense to fill in or outline nicely, so I thinned them with the gels & then they were prefect.
I mixed my black frosting with a lot of white gel to make the gray for Thomas' face. I did my final Thomas on a store-bought cake frosted white with no decorating. I sprayed the edges with Wilton color mist. I forgot to cover the rest of the cake before spraying, so there was some over-spray, but it was very light and turned out to be helpful.
I did the outline all in white gel as before. You have to put decent pressure on the parchment to get all the gel to transfer. There were a few areas that didn't, but I could see the outlines in the blue spray. I went over the outline on the cake in the correct colors and let it dry overnight. The next day, I filled in all the spaces. I used a toothpick to get the frosting into tiny corners.
I did the steam by the wheels after that dried & swirled it with my finger to make smoke billows. After everything dried I did a few of the outlines again. I did the writing last.