The Original: Neg and Pos Dupes
If the film has been shot on 16mm reversal, like Ektachrome, when you have a satisfactory answer print there are two courses you can follow if you want to make a dupe.
Dupes from Ektachrome originals
You can either make a duplicate reversal Ektachrome master or you can make a negative from the reversal original. To make a duplicate reversal master the laboratory simply re-expose the cut original on duplicate master reversal colour stock. Copies can then be made by printing the duplicate master on reversal stock. Alternatively, you can have the original cut colour master printed on colour negative stock, thus making a colour negative from which further copies can be made by printing on colour positive. If, for example, your film was shot on 16mm Ektachrome, you can either print the cut Ektachrome on dupe Ektachrome stock to make a master dupe and then print the processed master dupe on ordinary reversal colour stock to make subsequent prints, or you can print the cut Ektachrome original on Eastmancolor negative stock and then print the processed Eastman colour negative on Eastman colour positive stock to make your prints. The negative method has several advantages. It is usually cheaper to make prints by printing colour negative on colour positive than it is to print colour reversal on colour reversal, and contrast can be more accurately controlled.
Dupes from black and white originals
Preparing duplicates for 16mm films shot in black and white is also a simple process. For films shot on black and white negative a duplicate negative must be made. This cannot be done in one stage, like the colour negative process. An intermediate positive copy must be made. The original cut negative must be re-exposed on a low contrast fine grain positive stock, known as a fine grain dupe pos. The duping positive can then be developed and itself be re-exposed on a reel of duplicate negative stock. Copies of the film can then be made by printing the duplicate negative on black and white positive stock.
When an original is shot on 16mm black and white reversal there is again a choice of systems. A duplicate reversal master can be made by printing the cut reversal original on duplicate reversal stock. Copies can then be made by printing the dupe on other reversal stock. Alternatively the cut reversal original can be printed on negative stock. The processed negative can then be printed on positive film to make further copies. The neg/pos method has the advantage of making prints cheaper.
1. Colour reversal originals
From a colour reversal original (like Ektachrome) (A) you can make an Ektachrome dupe master (D) which can be used for making colour prints on reversal stock IE). Alternatively, you can make a colour internegative (B) which can then be printed on colour positive stock (C). The latter method enables you to produce copies at lower cost.
2. Black and white reversal originals (A) can be printed on black and white reversal stock (B) which can be used for making further copies on reversal stock. Alternatively, a black and white negative (C) can be made from the reversal original. The negative can then be printed on black and white positive stock (D). The latter system results in better and cheaper prints.