Rendering design prototypes for many materials can become easy once you learn to *predict* how the material will behave in given lighting conditions.

However highly reflective and transparent materials are much harder to predict – glass, in particular. That said, I notice many marker visuals for perfume bottles and glass products online that have been rendered very well without a reference (see Fig. 1-3). This leads me to believe that glass can be understood well enough to create convincing design constructions & prototypes if one knows how.

**Are there any rules to help me understand how light behaves on glass objects?**

i.e. **How do shadows & highlights behave on glass?** How can I anticipate the shape of reflections on a glass object? Does convex or concave glass effect how shadows/highlights/reflections are formed respectively? It seems that light is hardest to predict where glass is thicker, or where curves & edges occur.

I would like to be able to draft glass design prototypes that are more convincing, *without the limitation of existing glass references.*

I've included some examples below which demonstrate glass prototyping very effectively. These were designed by Sangwon Seok & Begüm Tomruk (see references & links below).

[![enter image description here](https://i.stack.imgur.com/Zp09S.jpg)](https://i.stack.imgur.com/Zp09S.jpg)

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Image References:

1. Sangwon Seok, (2014), Product Sketch [ONLINE]. Available at: <https://www.behance.net/gallery/product-sketch/14568139> [Accessed 5 September 2016].
2. Sangwon Seok, (2016), Product Sketch [ONLINE]. Available at: <https://www.instagram.com/p/BFV65usOEp8/> [Accessed 5 September 2016].
3. Begüm Tomruk, (2011), I.D. Sketching & Marker Rendering [ONLINE]. Available at: <https://www.behance.net/gallery/1176939/ID-Sketching-Marker-Rendering> [Accessed 5 September 2016].\*