[[Image:BlueDiamond.jpg|thumb|left|150px|The ''[[Blue diamond]]'' for lifetime warranty.]]
[[Image:BlueDiamond.jpg|thumb|left|150px|The ''[[Blue diamond]]'' for lifetime warranty.]]
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Despite the commercial success and the good technical quality of its pens, the [[Parker]] continued to invest heavily in research and innovation, and in [[1941]] introduced a revolutionary model, the [[51]], between the first pens made of plastic (''[[Lucite]]'') with a characteristic [[hooded nib]], which is necessary for the use of a new quick drying ink (the ''[[Superchrome Ink]]''), which tended to degrade the celluloid. The pen, although could not be considered particularly beautiful, and despite being built in ordinary plastic, was a tremendous success, and is probably the most sold fountain model of all time.
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Despite the commercial success and the good technical quality of its pens, the [[Parker]] continued to invest heavily in research and innovation, and in 1941 introduced a revolutionary model, the [[51]], between the first pens made of plastic (''[[Lucite]]'') with a characteristic [[hooded nib]], which is necessary for the use of a new quick drying ink (the ''Superchrome Ink''), which tended to degrade the celluloid. The pen, although could not be considered particularly beautiful, and despite being built in ordinary plastic, was a tremendous success, and is probably the most sold fountain model of all time.