I have loved cooking since a young age and have enjoyed experimenting with different ingredients in the kitchen. Salt is one of the most essential ingredients in cooking, yet most people never consider the differences between various salt types or pay attention to their distinct chemical compositions and structures. Through this post, I aim to examine not only the salts commonly used for cooking but also those found in laboratory settings. I will observe the crystal structures of different salts under my foldscope and explore whether their microscopic formations may influence salt taste.

Figure 1: NaCl (99.5%) for lab use ; mounted on a glass slide; 140X magnification plus 2x zoom on phone

Figure 2: Iodized Salt used for cooking; mounted on a glass slide; 140X magnification plus 2x zoom on iphone

The first two salts that we looked at are NaCl (used in laboratories) and iodized salt that is used in everyday cooking. Both iodized salt and NaCl (for lab purposes) look pretty identical under the foldscope. The only difference I saw was that iodized salt was comparatively more irregular in size and shape compared to NaCl. 

As a non-science major, I was curious to know if these two are almost identical in their chemical formula and structure and the foldscope, why is it that we can’t use the 99.5% NaCL in cooking? To answer this question, I asked a professor at NYU Shanghai for which I was told that NaCl which is 99.5% pure needs to be further purified for cooking, iodization provides the needed iodine to purify and remove elements without altering NaCl properties. Also, Iodized salt only has a small percentage of potassium iodide which could be a possible reason for why the basic crystal structure at a microscopic level appears to be the same. 

Figure 3: Pink Himalayan Salt; mounted on a glass slide;140X magnification plus 2x zoom on iphone

Since I was exploring salts commonly used in cooking, I also examined pink Himalayan salt under the foldscope to investigate if its microscopic structure relates to taste. I hypothesized that pink salt crystals may exhibit hints of their characteristic soft pink color. However, under magnification their color appeared predominantly off-white with occasional orange flecks. The crystals and grains showed an irregular, jagged texture unlike the smooth cubic shapes typical of refined table salt. This difference in morphology could result from pink salt often being coarsely ground, such that irregular grain particles rather than well-formed crystals were visible. Minor mineral impurities like iron within pink salt likely disrupted orderly crystal formation, leading to its non-uniform appearance at the macro scale.

The looser microscopic structure of the salt could also translate to slower dissolution versus denser refined salt, prolonging the flavor release. These natural mineral components impact flavor beyond solely sodium and chloride ions, imparting subtle sweetness or earthy tones. In general, salt readily absorbs moisture at surfaces, causing grains to appear cloudy rather than crystalline clear under magnification. This effect was exaggerated in pink salt, attributable to its higher mineral content. The desultory solubility could account for pink salt's less abrupt salty sensation on the tongue compared to refined salt.

While non-visual factors also influence taste, the textural variances between pink and refined salt at the microscopic level support pink salt having a less intense yet richer, more nuanced savoriness stemming from its indigenous mineral composition. 

Figure 4: Blue Salt (CuSO4.5H2O); mounted on a paper slide; 140X magnification plus 3x zoom on iphone

Lastly, I wanted to further analyze colored salts and since the color for pink salt was off-white, I wanted to see if we’ll ever see different colored crystals. Hence, I decided to analyze blue salt (or CuSO4.5H2O - copper(II) sulfate pentahydrate). Under the scope, the crystals were distinctly azure blue which would be due to the copper ions present in the formula. Unlike pure sodium chloride, the copper sulfate does not form neat cubic crystal structures. Its shape is irregular and fragmented. As a pentahydrate, it contains water molecules integral to its structure. This disrupts orderly crystallization patterns. Similar to pink salt, it readily absorbs atmospheric moisture, appearing lightly frosted under the lens. It is important to note that this salt is not used for any cooking purposes, and the analysis for blue salt was done under the supervision of a Chemistry Professor at NYU after adhering to strict safety and hazard guidelines. So, please do not try this at home. 

Another salt that I read about was the Iranian or Persian blue salt ( Cu(C2H3O2)2.) Due to the components, the Government of China has not allowed testing of these components which is why I wasn’t able to secure it and analyze it under the foldscope. Unlike blue salt for laboratory purposes, this iranian blue salt is often used for cooking purposes specifically to add artificial coloring in dishes. Since, I have already analyzed 4 different types of salts based on those I can infer that Iranian blue salt will have similar properties like irregular crystal structures, blue color due to copper ions. It may absorb less moisture and appear clearer under scope than heavily frosted copper sulfate grains. Also, commercial copper sulfate is likely less pure than intentionally food-grade Iranian blue salt, which would show fewer flecks or inconsistencies. However, these are just assumptions about the potential pattern for Iranian Blue Salt without the actual ingredient we cannot definitely analyze its components.

In conclusion, one thing common between all salts is that impurities lead to irregular crystal structures. While iodized salt and NaCl for labs have more clearly visible cubic structures (primarily because of the NaCl present) we do not see the same for pink and blue salt which have extremely fragmented crystal structures. 

Sources:
https://dhatuorganics.com/himalyan-pink-salt/
https://www.terreexotique.com/blog/persian-blue-salt#:~:text=Persian%20blue%20salt%20is%20rich,of%20the%20world's%20rarest%20salts.