The adhesive used to secure latex and silicone sacs to a section nipple must have certain characteristics. Among these:
• Good adhesion on such diverse materials as latex, silicone rubber, hard rubber, celluloid, aluminum, chrome plated steel, polystyrene, etc.
• Rapid cure time
• Lack of emission of harmful fumes
• Resistance to various liquids and the chemicals contained in fountain pen ink
• Reversability (easy removal without causing damage to the pen)
Historically, liquid Shellac (in particular Orange Shellac) has been the adhesive of choice, in that it is readily available, inexpensive and meets most of the requirements listed above. Some repair manuals have suggested the use of different adhesives, including rubber cement, cyanocrylate glue and clear nail polish.
Rubber cement has low adhesive power, hardens and decays in time and cyanocrylate glues are hydroscopic and will absorb moisture from the ink and eventually fail. In addition, they mar many plastics.
Clear nail polish is widely used by pen repair amateurs.
There are several reasons for not using nail polish:
• Nail polish contains acetone. Acetone emits fumes that can affect several plastics and that are very aggressive to celluloid. Those fumes in a small-volume enclosed space like the inside of a pen barrel can and probably will have a detrimental effect on the barrel plastic (even worse in celluloid pens).
• Nail polish does not soften at relatively low temperatures as shellac does. The application of Shellac is easily reversible.
• Removing dried nail polish from a sac nipple is not as easy and risk-free as removing shellac. One often needs a small file and that means taking away some nipple material.
• Some nail polishes craze with age and turn into a fine powder that ceases to have an adhesive effect on the sac and can actually clog a feed.
Top quality shellac is clear and extremely pure and uses only the purest alcohol-based solvents, which are safe for use in fountain pens. Shellac-based Sac Cement is easily removed with moderate heat, has superb adhesion even with silicone sacs and can be used for securing loose trim rings and other small metal parts. Any excess adhesive is easily removed with a cloth moistened in household alcohol.