Bayer Xantopren VL is a silicon used for dental imprints and it is quite tolerated by living surfaces, but you need a porometer to relate images to conductance as opening may vary under different light, CO2 and humidity. Details in Lawson et al JEB 1998 vol 49

Dear Karl Benton Svatos 

Please have a look following link. It may be helpful

Article Effects of High Salinity on Physiological and Anatomical Ind...

Stomatal density varies between monocots and dicots, between plant species, and between the underside and top side of the leaves on a plant.There are a number of ways to measure stomatal density, and the different techniques are explored here. One popular method has been to use clear nail varnish to make an impression of the epidermis. Other methods include using Germolene New Skin and using a water-based varnish from DIY shops. In this 3 minute video, Prof Alistair Hetherington  introduces 'The Mystery of the Evolution of Stomata'

A comparison of three methods for determining the stomatal density of pine needles ,J Exp Bot (2001) 52 (355): 369-373., DOI: https://doi.org/10.1093/jexbot/52.355.369

Abstract : Alternative methods were compared for determining the stomatal density of needles from two pine species. Densities estimated from air‐dried, whole needles using a binocular dissecting scope were compared to densities estimated from vacuum‐dried, intact needles using a scanning electron microscope and expanded peels (or macerated cuticles) using a compound light microscope. Differences among methods were expected from two sources: (1) expansion and shrinkage as a function of water content, and (2) differences in geometry of the measured surface. Estimates from the dissecting scope were similar to those from scanning electron microscopy (t=0.509, n=21, P=0.62), presumably because both used dried, but otherwise intact whole needles. Light microscopy estimates, however, were lower than dissecting scope estimates (t=−2.307, n=13, P=0.04). After adjusting for expansion due to hydration and changes in needle geometry, differences disappeared (t=−1.205, n=13, P=0.25). These results are an important consideration for researchers reconstructing palaeo‐atmospheric conditions and assessing plant response to environmental change.

Digital image processing for measurement of stomatal aperture (Plant and Cell Physiology 25: 1379–1388. – DOI:https://doi.org/10.1093/oxfordjournals.pcp.a076848 –

Abstract;We developed a new digital image processing technique for exactly measuring the degree of stomatal opening, that is, the ratio of the width to the maximum length of a stomatal pore, and the pore area. We applied this technique to evaluate responses to SO2 of neighboring stomata in a small region of an intact attached leaf, with the following results: 

The pore region could be exactly extracted even when the original digital image was of poor quality. The standard errors in the evaluation of the pore area, the pore length, and the pore width were 10 μm2, 0.3 μm and 0.3 μm, respectively.

A wide variety of responses to SO2 was found among neighboring stomata in a small region of an attached leaf. The differences were especially remarkable before water-soaking and wilting. When these began, k1 showed a local maximum value, and then all the stomatabegan to close. These results suggest that stomatal responses of intact growing plants to air pollutants should be examined from the standpoint of not only the average movement of many stomata but also the movement of each stoma and that the interrelationship among movements of neighboring stomata should be investigated to clarify the mechanism of stomatal responses to air pollutants.

Hi Anoop.

Thank you very much for the 2 reference links...

I have reviewed these publications and read them quite thoroughly but I am surprised no one has published in the space of digital stomatal measurement (real time live measurement )since 1984 given the leap in technology available!

I guess perhaps that digital technology hasn't changed much as a function of overall output but in terms of usability the areas of digitial photography and microscopy have changed astronomically!

The nail polish method looks accurate enough too but adds additional bulk sampling time restraints that make the method laborious.

Hence the initial question about measurement in real time on the plant.

Cheers from Aus!