Uranyl formate is a fine yellow free-flowing powder occasionally used in transmission electron microscopy

Transmission electron microscopy

Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...

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It is occasionally used as a 0.5% or 1% aqueous

Aqueous solution

An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending aq to the relevant formula, such as NaCl. The word aqueous means pertaining to, related to, similar to, or dissolved in water...

 negative stain

Negative stain

Negative staining is an established method, often used in diagnostic microscopy, for contrasting a thin specimen with an optically opaque fluid....

 in transmission electron microscopy (TEM) because it shows a finer grain structure than uranyl acetate

Uranyl acetate

Uranyl acetate is the acetate salt of uranium and is a yellow crystalline solid made up of yellow rhombic crystals and has a slight acetic odor. Uranyl acetate is slightly radioactive, the precise radioactivity depends on the isotopes of uranium present...

. However, uranyl formate does not easily go into solution

Solution

In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

, and once dissolved, has a rather limited lifetime as a stain. It is quite sensitive to light, especially ultraviolet light, and will precipitate

Precipitation (chemistry)

Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...

if exposed.