Mastering Glass Refraction: Nano Banana 2 Coffee Cup Steam Prompts

Generating images where a coffee cup appears to be made of clear glass requires more than just stating the material. The AI must understand how light bends through the medium, how the background distorts behind the liquid, and how steam interacts with the transparent surface. When using Nano Banana, which refers to the AI image generation tool rather than any physical product or brand, users can leverage specific prompt engineering techniques to achieve these complex optical effects. The goal is to move beyond opaque renderings and create visuals that mimic real-world physics, ensuring the glass looks transparent with realistic refraction.

The core challenge lies in defining material properties explicitly. Without detailed instructions regarding transparency, thickness, and light behavior, the model may default to ceramic or plastic textures. By focusing on the interaction between the hot liquid, the rising vapor, and the refractive index of the glass, you can guide the generator toward high-fidelity results. This approach is particularly useful for marketing materials, product mockups, or artistic compositions where the clarity of the vessel is central to the narrative.

Defining Material Properties for Optical Accuracy

To achieve true glass transparency, your prompt must describe the physical characteristics of the object rather than just its appearance. You need to specify that the material is clear, thin-walled, and possesses a high refractive index. This distinction helps the model differentiate between a simple outline and a volumetric object that bends light. For instance, mentioning the distortion of background elements visible through the cup is crucial. If the background is not described as being warped or magnified by the curvature of the glass, the result will likely look flat.

Furthermore, the temperature of the contents plays a vital role in the visual output. A steaming cup implies heat, which affects the density of the air around the rim and the way steam curls off the surface. In the context of Nano Banana 2, which supports text-to-image workflows, combining these thermal cues with material definitions creates a cohesive scene. The prompt should explicitly state that the glass is transparent and allow the viewer to see the liquid level and color through the walls. Avoid vague terms like "shiny" or "clear" without context; instead, use descriptors like "optically clear," "distorting background," and "specular highlights." These keywords signal the model to apply complex lighting calculations necessary for realism.

Five Distinct Prompt Strategies for Glass and Steam

Below are five materially different usable prompts designed for various scenarios. Each example targets a specific aspect of the glass and steam interaction. Please note that these are examples of prompt structures; they do not guarantee identity, label, object, or typography preservation, nor do they ensure identical outcomes across different runs.

1. Minimalist Studio Shot

Prompt: "A single clear glass coffee cup filled with black coffee, sitting on a white marble table. The glass is optically transparent with visible refraction of the marble pattern through the curved sides. Thin wisps of white steam rise gently from the rim. Soft studio lighting creates sharp specular highlights on the glass edge." When it helps: Use this when you need a clean, commercial-style product shot where the focus is purely on the object's form and material quality without distracting backgrounds. Adjustment: If the glass looks too thick, add "thin-walled" to the description. If the steam is too dense, change "wisps" to "faint vapor."

2. Dynamic Action Shot

Prompt: "Close-up action shot of a hand holding a transparent glass mug. Hot coffee inside causes significant refraction of the fingers visible through the glass. Thick, swirling steam clouds obscure part of the handle. Dramatic side lighting emphasizes the texture of the steam and the glossy surface of the glass." When it helps: Ideal for lifestyle imagery or social media content where movement and human interaction are key. This style captures the energy of a morning routine. Adjustment: To increase the sense of motion, add "motion blur to the steam" or "dynamic angle." Ensure the hand does not look distorted if anatomical accuracy is required.

3. Macro Texture Focus

Prompt: "Extreme macro photography of a clear glass coffee cup rim. Water droplets cling to the outside surface due to condensation. Inside, dark coffee reflects light. Steam rises in tight spirals, interacting with the droplets. High detail on the refraction of light passing through the water droplets and the glass wall." When it helps: Best for artistic close-ups where texture and minute details are the primary interest. This works well for wallpaper or high-resolution print assets. Adjustment: If the droplets are missing, emphasize "condensation" or "sweating glass." To enhance the steam, specify "volumetric fog."

4. Atmospheric Background Interaction

Prompt: "A clear glass coffee cup placed on a windowsill with a blurred city skyline in the background. The glass refracts the colorful sunset lights, creating rainbow-like distortions on the table. Warm steam drifts upward, blending with the ambient light. Cinematic depth of field." When it helps: Perfect for mood pieces or storytelling where the environment contributes significantly to the atmosphere. The refraction here serves to integrate the object into its surroundings. Adjustment: If the background colors don't appear in the glass, add "chromatic aberration" or "color dispersion." To make the steam more visible against the bright sky, specify "backlit steam."

5. Abstract Light Play

Prompt: "Abstract composition featuring a transparent glass cup filled with amber liquid. Strong beams of sunlight pass through the cup, projecting complex geometric shadows and refractions onto a wooden surface. Steam is minimal but catches the light rays. High contrast and sharp focus on the light patterns." When it helps: Useful for graphic design elements or abstract art where the physics of light is more important than the literal depiction of a coffee cup. Adjustment: If the shadows are too faint, request "hard shadows" or "sharp caustics." To reduce the complexity, simplify the background to a solid color.

Model Selection and Workflow Considerations

Choosing the right variant of the tool is essential for achieving these specific visual goals. Nano Banana 2 is identified as Gemini 3.1 Flash Image, while Nano Banana Pro corresponds to Gemini 3 Pro Image. Google describes Nano Banana 2 Lite as focused on speed and cost, noting it is not optimized for multiple reference inputs or multi-turn sequential editing. Therefore, for complex tasks involving detailed refraction and steam physics, relying on the standard Nano Banana 2 or Pro models is advisable over the Lite version, which might struggle with the nuance required for optical accuracy.

It is important to remember that prompt instructions describe desired outcomes but do not guarantee identity, label, object, or typography preservation. Users should treat the generated images as starting points for iteration. If the first attempt lacks the desired transparency, refine the material descriptors rather than changing the entire subject. For those ready to experiment with these techniques, you can Try Nano Banana to access the text-to-image workflow directly.

By carefully constructing prompts that define material properties and environmental interactions, users can consistently generate high-quality visuals of glass coffee cups with realistic steam and refraction. This method ensures that the final output aligns with the intended aesthetic, leveraging the capabilities of the underlying AI models effectively.