Here is how I make a mosaic quilt.
First, find some scrap fabric and draw your design on it. You need a line wherever you are going to use a different color. If you draw in the wrong place, just X out the line so you know not to pay attention to it. No one will see this.
You are going to glue these down to the base fabric, but DO NOT glue all the way to the line. Here you can see where I put glue down. I do a mix of gluing the base fabric and putting glue on the fabric I'm putting down, but it is easiest to avoid the lines if you glue on the base fabric.Use washable glue sticks. If you get them at back to school time, they cost a fraction of the rest of the year.
Fill the whole area, going OVER the lines. Use lots of small pieces. Or if you want a non mosaic look, you could just use one big piece, but this technique probably isn't the one for you.
Now, carefully cut all the fabric away so that it is exactly on the line. I found using small applique scissors made this the easiest.
Here is why you didn't glue all the way to the line. Tuck the next color of fabric UNDER the first color.
When you are done filling this color, trim again to the lines.
Keep going until the entire fabric is filled.
Now, you need to make a regular quilt sandwich- backing, batting, and this is your top. I originally layered with tulle but I received some advice that it muted the colors too much, so halfway through I switched.
Let's talk about tulle first: To make the tulle "hide" you need to quilt very dense microquilting. This holds down all the fabric, and it also puts enough thread on the fabric that you can't see the thin layer of tulle without looking really hard. This also holds down any fraying and makes the raw edges basically not raw. But it does mute the colors; but you could experiment and try different colors of tulle and see what they do.
The front of the quilt is still a secret, but here is the back of one of them after quilting. You can see how tight it is over the tulle.
Please let me know if you use this technique or if you have any questions! I'd be happy to answer them. Stay tuned for the final quilt.