How can I repair a Coticule?

Coticules are natural rocks. As such they are normally fairly low maintenance. They don't glaze, don't require frequent lapping, don't de-laminate, they're as good as impermeable and they don't mind if you put water, oil, silicone lubricants or whatever on the surface. (some caution with acids would be in order though). But even so, some issues can sporadically occur. In this FAQ we offer an organized list of  possible problems and their solutions.
 
1. GLUE line separation
2. Natural separation
3. Cracks
3.1. Lateral cracks
3.2. Transverse cracks
3.3. Longitudinal cracks
4. Inclusions
5. Chips

1. GLUE line separation

The joint of a Coticule produced with nowadays methods is not expected to ever fail, since it uses a modern high performance, fully waterproof cement, similar to products used for swimming pool tiling. However on older specimens, that were glued several decades ago with less stable glues, it is almost predictable that the joint may fail at some point, given enough time to decay (100 years, plus or minus a couple decades).
When and if this happens, there is no need to panic. With the glues readily available on today's market, it's easy to bond both pieces back together. It is important that both pieces remain intact. Should haplessly the blue backing plate be broken, you could opt to glue the Coticule part to another backing: a tile, a paddle shaped piece of wood, or - if you want to honor tradition - a new piece of BBW. Should on the other hand the Coticule part be broken in 2 fragments, you can try to reassemble, but there is no guarantee that the transverse joint won't interfere with the functionality of the hone. For a solution of that problem, see the paragraph about transverse cracks below.

Recipe:

First you need to scrape all the old glue off of both fragments. It's a hide glue based adhesive, hence heat will soften it up. A hot air gun as used for stripping paint or even a plain hair dryer will help to soften the glue so you can take it off. As said, be extremely cautious not to snap the pieces. While working, the parts must be completely supported by your working surface. If the parts are not flat (old Coticules often separate during the lapping process), they can be supported on a plastic bag filled with damp sand.
Once you have both the surfaces to be rejoined clean (a bit of sanding might be in order), make sure they are dry before you continue to glue them back together. Almost any glue with filling capacities and reasonable water resistance will be suitable. Thin-set tilling mortar, skirting board adhesive, 2-component epoxy, glue-gun hot glue; are all capable of rejoining a Coticule with its blue backing plate. Follow the instructions of the product at hand. In general, apply a liberal amount of glue on one part (make sure it's well supported), use a small glue comb to corrugate the coat of glue, and put the second part on top with a small sliding motion to assure an even and fully filled glue joint. It's good if some excessive glue squeezes out at the sides. Scrape most of it off and lap the rest away later, when the glue is fully cured. In case of hot glue, preheat the parts with a hairdryer to buy some extra handling time.

2. Natural separation

In case of natural separation, which means that the Coticule separated at a lateral crack, either at the natural transition between the yellow and the blue part (which is the most prevalent occurrence of this rare problem) or at a crack present in the Coticule itself, the pieces will in 99% of cases still fit tightly together. If so, they can easily and perfectly be rejoined with CA glue (cyanoacryclate, also known as wonderglue/superglue).
In the unlikely event that the parts can't be tightly fitted together, refer to paragraph 1 of this FAQ-article.

3. Cracks

3.1. Lateral cracks

Lateral cracks are cracks that show up at the narrow side of the hone. Often they can be squeezed together a bit and spring back when the force is released.
Sometimes such cracks run diagonally in the stone, to emerge as a longitudinal crack at (part of) the surface. If this happens the stone can be impossible to lap flat, because the lapping forces compresses the crack, only to spring back afterwards. This leaves you with an ever so slight raised part of the surface, which of course interferes with the honing functionality.

Recipe:

Option 1: Put the hone on its side, and use a couple of toothpicks to minimally pry open the crack. Pour in CA-glue, or even better use a syringe with needle to get it in. (Please wear safety glasses, you don't want to accidentally have high-pressured CA-glue spraying in your eye!) Try to get in as much as possible. Ideal is when some of the glue starts emerging out the other end of the crack (if the other end is exposed). Remove the toothpicks and place the Coticule between a clamp, applying only the gentlest pressure. Give the CA-glue a day to cure. In a tight fit, CA-glue dries within seconds, but when it needs to fill the joint a bit, it takes considerably longer to cure. If the crack is expected to remain open for more than 2/10 ths of a mm, use special CA-glue with filling capacity. Or refer to option 2.

Option 2:

For larger cracks it is better to fill them with a hot glue. You can either use the sticks of a glue-gun type of hot glue, or prepare your own glue sticks according to the traditional composition. For this, melt together hide glue and beeswax (50/50) and pour it with aid of a funnel into paper tubes that you need to prepare for this purpose. To do so, roll a sheet of paper on your finger, using several revolutions. Fold the bottom 2 times, so that it can hold the glue once you pour it in and completely secure this cylinder with paper masking tape. Once the glue is poured in, allow to cool in upright position.
The use of these homemade hide glue/beeswax sticks is the same as glue-gun sticks:
Place the Coticule dry in an old skillet, and heat on a slow burner. Once it is hot enough, the Coticule will melt the glue as soon as you touch it with the stick. (Do not use the glue gun, but allow the Coticule to melt the glue by itself) Place the Coticule with the crack facing up and allow the glue to run into the crack. The heat will often cause a crack to open a bit further. Never try to hasten the cooling of a hot stone! Allow the stone to cool naturally in the skillet, rapid cooling of hot stone can cause it to shatter.
If you are using this method on an old Coticule, the glue that holds both parts together is the same as the hide glue/beeswax mixture. In this case you need to take special precautions to prevent the separation of both parts. Wrap the hone very tightly in several layers of aluminum foil, but as you make each wrap, use a sharp knife to make small incision of about 25mm along the crack somewhere in the middle. You need to end up with a tightly wrapped Coticule with only a small incision in which you will pour the glue. Fold the incision open a bit to properly expose the middle part of the track. If the crack comes out somewhere else, also make small incisions there to help evacuation of air, as the crack fills with glue.
Once cooled, trim of excess glue and lap the stone flat using a Diamond plate or wet and dry type sandpaper.

3.2. Transverse cracks

Transverse cracks are cracks running across the surface of the Coticule. They are not to be mistaken with Manganese lines, that are not cracks and have no negative influence on the functionality of the hone. Transverse cracks become annoying when the edge starts catching into them as it passes over during the honing stroke. This can be sensed very well, and obviously causes damage to the edge.
The solution isn't ideal as you will likely still notice the crack as it will give a slightly different feedback after the applying the fix, but the Coticule can be expected to function again.

Recipe:

Take a square wooden block with sharp edges and fold a sheet of 80grit sandpaper around. Put the sanding block with one edge on top of the crack and start sanding. The goal is to replace the crack with a 2 mm deep V-shaped groove. A filler can be made from CA-glue, mixed with Coticule dust. You'll need more Coticule dust than the one you got from creating the groove. Prime the groove with CA-glue and immediately apply the filler. Try to heap it up a little. Allow at least 24 hours to cure. Carefully lap the stone in a direction along with the prior crack, as to not stress is too much.
An alternative filler is to first fill the groove with baking soda (this is not the same as baking powder, baking soda is sodium bicarbonate) and pour CA-glue on top. Both respond to each other with an exothermic reaction, forming a hard filler.
Another excellent filler is to mix a quantity of Coticule powder with 15% (by volume) artistic plaster (plaster of Paris) Add egg yolk until the paste is soft and workable This allows a barely visible repair known to not affect the edge being honed.

3.3. Longitudinal cracks

Longitudinal crack are cracks than run lengthwise or almost lengthwise in the surface of the Coticule. They will usually not have any ill effects on the performance of the hone, and we suggest leaving them as is. For some ease of mind, they can be treated as lateral cracks, either by pouring in CA-glue, but without prying them open, or by the "hot skillet" procedure. Turning them into a groove for filling with any of the recipes explained at the paragraph about the treatment of transverse cracks will generally not be necessary.

4. Inclusions

Although a rare occurrence, it can happen, as the Coticule slowly wears down throughout the years of use, that a foreign fragment of rock emerges at the surface. Due to the composition of Coticule rock, this is in the majority of case any of a number of possible mineral crystals that are all considerably softer than steel, and mostly even softer than the overall hardness of the Coticule stone. In these cases there is no effect on the honing properties of the stone and nothing should be done. If however you experiences a hard clicking sound when the edge passes over the anomalistic particle, it is likely doing damage to the edge. This can be revealed by inspecting the edge under magnification. If this happens you will need to dig out the foreign particle. With aid of a loupe and good lighting it is not that difficult to dig out the particle with a needle. The tip of a needle can dig into the rock surrounding the hard particle easier than you might have expected and eventually the particle can be pried out. The resulting void can be left as is, or filled with one of the fillers from paragraph 3.2 - Transverse cracks.

5. Chips

Chipping can occur at the surface of a Coticule near the edge. If you see first signs of it, is best to create a more pronounced rounding of the hone's edges. This can easily be done with 80 grit sandpaper on a sanding block. Further smoothing with finer sandpaper is recommended.

Last update on 2011-04-12 by Ralfy.

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