Iconographic grids are an essential part of the process of making Thangka paintings. These grids are used to ensure that the proportions of the figures in the painting are accurate and consistent with the iconography of the deity being depicted.
The necessary gridlines include a central perpendicular line and two diagonals, among others. The artist uses these guidelines to learn proportions, but after years of practice, they rarely employ them. The grids are drawn on the canvas using a pencil and are used to sketch the figures in the painting. The artist then paints over the penciled drawings with a fine brush and later fills in the colors.
I hope this information helps! Let me know if you have any other questions.
Source(s)
1. Process of Thangka Painting | Project Himalayan Art
3. Thangka Painting Revealed: History, Types, Techniques, and Preservatio
4. The Origins of Thangka Painting – Tretyakov Gallery Magazine