This is a chapter of my upcoming book, tentatively titled "The Art of Fire Transfer," which I thought I would include here.
Background and Commercial Manufacturing Process:
I was unable to find anything about the manufacture of Visco in any of my books, so I e-mailed a friend in the fireworks trade (who doesn't want his name mentioned) about the subject. He explained the process in detail and was quite helpful. Here is his reply:
OK, I'll give you the quick-&-dirty. You'll find little in the popular literature about fusemaking. There is a little in the technical literature pool, but you've really got to work to find it.
The modern "textile fibres wound around a black powder train" fuse was developed in Wales (UK) for the Cornish mining interests. A reliable but cheap fuse was needed and somebody just designed the machinery to do it. A later refinement was adding the heavy water-resisting coat, which, for some unknown reason, they called "Visco". I suspect it was some kind of early plastic-type,water-resistant chemical. (Originally it was made with a dextrin-based coating.) Today, of course, lacquer with red or green dye added, is the coating material.
The fuse was imported by our blasting industry and quickly caught up by the makers of "American salutes", those classic 2" and 3" machine-made firecrackers. The fuse was perfect for use in machine operations.
The design is now well in public domain. It's relatively simple. A steel frame in an L shape supports a funnel at top and several revolving platforms that contain spools of yarn. A special form of fuse-making black powder is poured into the funnel after the yarns have been positioned and ready to go. (This is a slowed-down BP with extra charcoal.) As the machine turns on, the yarns are pulled downward and made into a spiral form,at the same time that black powder is dribbling out of the funnel. In one design, one or more straight yarn strands are passing through the funnel and pulling the black powder in a measured fashion. (In the US, these strands are colour-coded to distinguish the maker's product from others.)
Anyway, here's the fuse powder coming out of the funnel and the yarns being spun around it. With all these spools turning and gears and cams going, it's a sight to see!
All this takes place in the upper arm of the L. As the fuse make a 90 deg. turn at the bottom of the L, it enters a trough that contains the coloured lacquer, and then proceeds into a drying tunnel through which hot, dry air is passing. The fuse goes down this tunnel for some distance (no less than 25-feet, and more in most cases), then climbs around a wheel and heads back to the fuse room. The total time spent in the drying tunnel is sufficient so that the fuse is dry by the time it re-enters the fuse room. There it is spooled onto a 10,000-ft. wooden spool.
The operation is dangerous because of the solvent used in the lacquer. Also, the finished fuse is under some tension and an accident can send flying, burning fuse all over the place!
It's been said that a good operator can work 3 machines at a time, although I have seen only one being operated at a time.
Ensign Bickford Co. was a principal supplier for many years but a bad lawsuit some years ago soured them on providing fireworks fuse. It is said that they destroyed their machinery and will never again permit their products to be used in fireworks.
There are two main suppliers of Visco fuse for the fireworks trade and a few fireworks manufacturers have their own machines and make for their own use. (There may be more than two. Also, a lot of Visco comes from China, but this fuse is slightly inferior.)
The manufacturer of the Visco fuse machines currently in use has died and no new machines have been made in decades, but one man in New York claims to have re-invented the machinery; last year he was offering to provide new machines for anyone wanting to get into the business. It is said that he sold a few to a certain fireworks company in Pennsylvania. I have seen fuse said to have been produced on his machinery and it is perfect Visco in every respect.
Hobby Syringe (syringe without needle)
I had a bit of a hard time finding these. I eventually found them at my local pharmacy, who sold them for the application of topical intra-oral medication. They usually cost about 25 cents, although the lady behind the counter gave me four of them for free. Also, I have heard that a farmer's supply store is a great place to look (the farmers use them for veterinary purposes).
Hollow-cored Cotton String
I buy hollow-cored string from a local art store, which sells it because it makes an excellent wick for oil lamps or homemade candles. It usually comes with another, somewhat thinner string threaded through the core to prevent stretching. This should be removed.
The meal powder that I had used was the homemade ball-milled variety. However, commercial meal powder from the local firearms shop works just as well.
I had used homemade dextrin in my Visco, but dextrin from health food stores or Skylighter works just as well.
25% Nitrocellulose Lacquer (optionally dyed green or red)
The nitrocellulose lacquer can be either homemade or bought from Skylighter. I used homemade. Also, adding a bit of camphor to the NC lacquer will plasticize the nitrocellulose after the solvent has evapourated, allowing for a more flexible fuse (the commercial plastic "Celluloid" is nitrocellulose plasticized with camphor).
1: Make Black Powder (BP) paste: Take 10 parts by weight of meal powder and thoroughly mix with 1 part by weight of dextrin (ie, mill it in a ball mill for half an hour). Boil some water and add it slowly to the BP/dextrin mix, while stirring, until the mixture has twice the consistency of white glue.
2: Remove the plunger from the syringe and plug the hole at the bottom with a thumb. Pour the BP paste into the syringe, filling it almost to the top. Reinsert the plunger and turn the syringe upside down, and depress the plunger until all excess air in the syringe has been removed.
3: Insert the nozzle of the hobby syringe into one end of the hollow core string and slowly depress the plunger so as to allow maximum consistency of BP paste in the center of the Visco, allowing for a more consistent burn rate. The string should ideally be 1 meter in length. Refill the syringe using the method outlined in step 2 whenever necessary. Continue injecting the BP paste until it is visibly exuding from the end opposite of injection. This means that the core is as full as it is going to get.
4: Remove the string from the syringe's nozzle and lay it down on a flat surface. Gently roll the string between the heel of one's hands and the flat surface to further even out BP paste distribution and increase burn rate consistency. Allow the string to dry outside in the sun for a period of 24 hours, turning the string over every hour or so to prevent the BP paste filler from becoming uneven.
5: After the filler has dried, apply a thin coating of 25% Nitrocellulose lacquer to the entire external surface of the string and allow it to dry in the sun. This will waterproof the fuse and allow it to be used in potentially wet situations.
6: Let the fuse sit in the sun for 24 hours after all the wet fuse components have dried to ensure minimum moisture content, which interferes with the burning of the fuse. Check the burn rate, and label each length of fuse with a sticker that indicates the exact burn rate of the particular fuse. This is not necessary but highly recommended as each fuse's burn rate may be different from the next one's.
7: The imitation Visco is now ready for use. It can be used wherever commercial Visco is used.
When I was injecting the BP paste into the string, I occasionally noticed it 'squirming' out of the weave of the string. This tells you that you are injecting the BP paste too fast. If you notice that this happens, slow down your injection speed. Also, wrapping the external surface of the string temporarily in masking tape seems to efficiently hold in the paste during injection. This means that using a faster injection rate than would normally be used is possible.
The fuse I made using the above outline instructions burns a bit faster than commercial Visco does. In the course of experimenting, I have found that binder-fuelled fuse comps burn slower than do BP or other comps, whilst still providing plenty of heat. Therefore, substituting a KNO3/Red gum composition in (m)ethanol (acetone dissolves the syringes) for the BP paste stated above would provide a slower burning, though just as reliable, fuse. Also, using less sulphur and more charcoal in the BP used for the BP paste will slow the burn rate. But, as the old adage goes, "to each, his own."
This section will detail the experience that others have had with my visco idea. Its purpose is to verify that the idea works and also to provide the reader with some knowledge that may not be present if only my experiences are included. Feel free to submit your experiences to me and I will gladly include them.