Certain manufacturers produce fixatives specified for a certain media only, such as soft pastel fixatives. The most common precipitating fixatives are ethanol and methanol. Resinoids are mainly used as perfume fixatives. When used in combination with alkaline fixatives, the fruit bodies can produce striking violet colors. Then, scent preserving fixatives (see below) were added. In addition to formalin, other chemical fixatives have been used. Dialdehydes, e.g. glutaraldehyde and malonaldehyde, are fixatives or sterilizers. Some fixatives also lead to complete loss of cells. Other fixatives used for electron microscopy are osmium tetroxide or uranyl acetate. Modern fixatives are usually alcohol based, and hydrocarbon propelled. The balsam and its oil are used as fixatives in soap perfumes and fragrances. Crosslinking fixatives act by creating covalent chemical bonds between proteins in tissue. Common fixatives include formaldehyde, ethanol, methanol, and/or picric acid. Fixatives generally preserve tissues (and cells) by irreversibly cross-linking proteins.