This project is a stretch. It really wasn't economic but it is instructive of a project that uses skills that might be useful in another scenario. It started when my wife dropped one of her ceramic canisters from a set of 3 and broke the lid and base. The lead photo shows the two remaining intact canisters with the damaged one. She says they are in demand and very valuable. They had better be 'cause it cost a lot to do what I did! Actually, the fix incorporated materials I already had for use in my many craft hobbies so out-of-pocket expenses were minimal. Someone doing it from scratch would spend in the neighborhood of $75 to $85 for all the necessary materials.
I made a reproduction lid complete with finial for the small canister.
Here is a list of most of the materials need for the project. As was my case, you are an Instructable fanatic so probably already have a lot of this stuff already.
Mold release spray. I use Smooth On brand
Urethane hard plastic casting kit. I used Smooth On
Fiberglass resin & mat kit. I used Bondo brand
Polyester body filler. I used Bondo brand
Popsicle stirring sticks
Disposable mixing cups
Optional talcum powder (explained in following step)
Spray primer and appropriate color of gloss enamel paint
Small saw such as a X-Acto razor saw
tubes of 5-minute epoxy
various grits of sandpaper
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Step 1: Making the Lid Mold
This project is complicated by the fact that all three jars in the set are different sizes so all the lids are too. This being the smallest lid, I had to figure out how to get an accurate smaller version of the two bigger ones. I decided to make a fiberglass copy of the next larger lid as a start. The first thing to do was to make a fiberglass mold of the original. Since the finial on the pattern lit is affixed permanently, it couldn't be removed so I had to build the mold around it. Also I added two clay dams down the sides of the lid so only half the pattern was made at a time. Lay up resin and fiber glass (3 layers of mat is perfect) on one half of the part. Let it harden then remove the two vertical clay dams and lay up the second half of the mold.
Some notes about fiberglassing;
1) it is much worse to use too little catalyst hardener than to use a little too much. Too little results in a partially hardener part and a big mess trying to remove it and start over. Don't skimp and don't be afraid to over treat.
2) Always spray the pattern with mold release spray before laying up the fiberglass and resin.
3) If by chance you used slightly too little hardener, try setting the part in direct sunlight. UV light reacts with the resin and usually hardens it.
4) Get some chip brushes and daub the resin on the part, place on a layer of glass mat, then daub out all the excess resin and air bubbles so the composite is thin and no air. Get a big box of chip brushes from Harbor Freight for a couple bucks. they are disposed after each use so you don't want expensive ones.
5) You must wait for the gel coat to harden completely before starting to layer on the mat and resin. The latter process can be done all in one session, no need to wait for the previous layer to harden.
6) Mix small batches of resin, try for just enough to do one layer of mat. Mixing too much risks the resin setting up before using it all. That isn't a disaster, just a bit wasteful.
7) Separating the mold from the pattern is pretty easy to do but does take a little effort, A pocket knife is a good tool to use because it has the sharp edge to work into the crack between the wings of the mold but the blade is stiff enough to not break when used to pry. Don't use an X-acto knife blade. BE CAREFUL, it is a knife after all! work the blade into the crack in several places and start to separate the pieces. You don't have to do it all at once in one place, work on several places around the joint and it will all of a sudden pop off. This is a fun process too.
7) Clean up uncured resin with acetone. Lacquer thinner also works but acetone is better.
8) Finally don't be afraid of fiberglass. It is easy and fun, just takes a but of practice to perfect technique. I have guilt entire car bodies with it in the past but still have to do a bit of retraining to remember all the techniques when doing it again after awhile. Try it, you'll like it.
You will note the orange color of the parts. This was due to my using a polyester resin called 'gel coat' that is a resin formulated to be tougher to handle the wear and tear on a pattern part from making many final parts. This was overkill for this project since I was only making one part but hey, I had the resin so might as well use it. You can make your own version of gel coat (it won't be the sexy orange color but will have some of its characteristics) by adding talcum powder to the resin before adding the catalytic hardener. A tablespoon of powder per ounce of resin should give you a nice result.
Photo 1 shows the fiberglass mold on the lid. Photos 2 and 3 show how I made the mold. I first used modeling clay to build a dam around the finial in top so the fiberglass resin wouldn't mess it up. Then I painted on a heavy coat of gel coat resin and let it harden. The 'wings' on he two mold halves accept spring clamps to hold the pattern together while making the new part.
The hardest part of fiberglassing is getting the mad to fill in tight corners and avoiding bubble-caused voids in the finished surface. Do the best you can, it isn't a disaster and can be fixed so no big deal.
The big hole in the top of the mold stays there, we will fix that on the final lid we make from the mold.
Step 2: Making the Final Lid Part
Now that we have a mold, we need to clamp the two parts together and spray them with a good coat of mold release. Paint a heavy coat of resin or your home made gel coat inside the mold and let it set. This will serve as the finished surface of the part and prevent the grain of the fiberglass mat cloth from 'printing' through.
After the gel coat cures, layer in ONE layer of cloth and resin. Again be as careful as possible to avoid air bubbles between the layers. Once this sets, pop off the mold.
Obviously this is not the final condition of the part, it is too thin. However remember, this lid is too large in diameter to fit into the small jar opening. It has to be shrunk. I did this with an X-acto razor saw by cutting out a wedge as shown in photo 1. I sawed the notch at a spot where the filigree around the waist of the lid would go back together as inconspicuously as possible. Remove the material carefully, squeezing the lid together and testing the fit until the lid fits into the smaller jar. Once the joint was correct I used clear packing tape to pull the joint tightly and uniformly together than used some 5-minute epoxy resin to glue the joint back together.
Now to address that gaping hole in the top of the lid where the finial was. O mixed some resin and laid in some strips of fiberglass matt from the inside of the part, lower than the outside surface of the lid but domed like it and let it set. Then using the Bondo body filler (with hardener of course!) I puttied in the void to about he shape of the hemisphere dome. This is art, not science. The I used 100 grit sandpaper to 'machine' the shape to a perfect hemisphere. It might take a few patch jobs with the polyester resin bit is easy to do.
Now that I had my new lit I laid in two more layers of mat and resin from the inside and let it harden. Finally I used Bondo and 220grit sandpaper to perfect the joint on the side of the lid and the hole in the top. Once it looks perfect spry it with the hi-build sandable primer. Once dry, go over the entire part carefully with 400 wet sandpaper. It's ok to sand through the primer, the purpose is to fill in imperfections, not build up a heavy paint layer.
Step 3: Making the Finial
To make this part the first step is of course to spray the finial on the pattern lid with mold release. Then using card stock and tape, male a 'housing' that surrounds the part with about 1/2" clearance between the card and the part. I spent time cutting the bottom of the card to fit the shape of the hemispherical lid to prevent leaks of the (expensive and messy!) urethane rubber resin. Photo 1 is a picture of the set resin with the card dam stripped off. Use modeling clay to seal the dam to the lid and anchor its position around the part.
Now just mix up some resin (I really like the Smooth On products. 1:1 mixing ratios by volume, mix easily and give consistent fool proof results.) and carefully pour it in the annulus between the part and dam. On a complicated part like this wit a lot of undercutting and niches, I like to pour in a bit of resin then use a popsicle stick to work it around the part to insure all the trapped air bubbles are worked out. Do the pour in stages like that. This stuff takes longer to set that the resins used to this point so let it set over night.
When the resin is cured, remove the clay and card stock. it will look like photo 1. To release the part form the rubber, use a sharp X-acto knife to slice one slit down the rubber, working the tip of the knife into the crevices of the part. Cut, pull, stretch until you get the result shows in photo 2. Photo 3 sows the finished rubber mold ready to cast the final part. Spray the mold with mold release, tape the slit together for a liquid tight seal then lix some urethane plastic resin (exactly like mixing the rubber resin) and using the same staged pouring techniques, fill the mold and let it set overnight.
Remove the rubber mold and you should have a perfect, white finial. the bottom will not fit the hemisphere shape perfectly so using some trusty 100grit sandpaper, machine the bottom of the part to fit the lid snugly.
Step 4: Finish and Assembly
At this point I recommend doing the final finish of the two parts. I was prepared to do some fancy paint mixing to match the red color of the pottery. However I found that Krylon red enamel paint matched exactly. Murphy was definitely sleeping on the job on this one. I drilled a 1/2" hole in the top of the lid with my pocket knife to allow gluing the finial on top then with the fine 400grit surface of the lid, three medium coats of Krylon enamel gave me a perfect finish.
For the finial I studied the original part ad determined they first sprayed it with silver paint then stained that with a dark color to achieve the aged patina. I sprays mine with aluminum paint then using a couple colors of oil-based wood stain wiped it until I achieved a reasonable match. Finally I used some 5-minute epoxy to glue the finial to the lid. Photo 1 shows the inside of the lid and the epoxy that fills in the hole and locks the parts together.
Step 5: The Result
Here are a couple shots of the finished lid. It is virtually impossible to tell the difference. I didn't attempt to make the base for the jar to match the other tow since that part is totally different from them and I couldn't extract the necessary shape and size. I think the finished part still fits the set even without the base.
As mentioned in the beginning, this project was probably not justified on a practical economic basis but it was fun and salvaged some junk from the landfill. And frankly, how many of our craft project are economically rational anyway?