Repairing cracks in china and glass

1 When an article develops a crack, the edges of the crack may be tight together or they may separate to some degree. On a tight crack the edges cannot be separated with the fingers. In this case, no action is necessary, but if the crack is loose and the edges can be moved out of alignment it should be treated as follows:

  1. Insert a razor blade into the crack about 1/8" to open it up wider. Use a rocking motion, rather than trying to press the blade straight down into the crack.
  2. Press cement into the crack thoroughly from both sides, using the index finger. When No. 200 is the cement to be used ( for dinnerware, glass, etc. ), always heat the article warm to the touch first. For ornamental articles, where No. 100 cement is to be used, do not heat the article. After cementing, remove the razor blade, again using a rocking motion. ( Be careful not to cut yourself. )
  3. Where possible, bind the article tightly with string or tape to hold together the two parts of the crack until the cement dries. If the edges of the crack are out of alignment ( one side higher than the other) at the rim, use a small C-clamp to press the edges even. Be sure not to tighten the clamp too much or it may break the article.
  4. Air-dry and heat the article in accordance with the instructions in the cementing procedures for the type of cement used.

2 Where a crack extends almost across an article to within 1/2” or 1" of the other side of a cup or plate it is best to snap the two pieces apart. It would be practically impossible to cement a crack of this length without separating the pieces as the cement could not be applied to the broken edges. For instructions see cementing procedures.

3 To repair a crack professionally, in addition to cementing, steps should be taken to prevent the crack from extending. A crack usually starts from the rim. If the article is a piece of dinnerware that is used quite often, the crack will get longer as time goes on, and if nothing is done, it will keep extending until the article is in two pieces. This is partly due to expansion and contraction resulting from washings in hot water, but the main reason is that each time a cracked article is set down a certain amount of vibration results. Stop the vibrations and you stop the crack from extending, even though the article is washed in hot water.

Cementing the crack helps to stop vibrations, but it may or may not stop them all. To be sure all vibrations are stopped, install a butterfly rivet or use the rivet method ( see below) on the crack at the rim location. Once a crack is locked together with a rivet at the rim location, vibrations are completely eliminated. This rule applies to all cracks, whether loose or tight.

4 On china 1/16" or less in thickness, a butterfly rivet is used to stop vibrations, and is installed as follows:

  1. Use a No. 2 wheel and gently grind anchor grooves into the edge of the china so that they extend completely through the thickness and show on both sides of the article, starting from the centre of the crack at the rim, and on an angle in the form of an inverted V. The length of each groove should be about 1/8". This grinding is done before cementing a loose crack..
  2. If the crack is loose, the cementing is done next. If the crack is tight, omit this step.
  3. After the cement has dried and been heated, the grooves are filled in with pewter. Pewter is used for this purpose because it is strong and will not break apart at the apex of the groove as a ceramic type of filler would. Also, pewter can be covered and made invisible when decorated just as easily as any ceramic mixture.
  4. With the hard carbide rubber wheel in the hand grinder, smooth off any excess pewter until it is even with the surrounding surfaces. Wash the rivet with soap and hot water, and air-dry for at least one hour. Then give the rivet a coat of No. 100 cement. Air-day for three hours or force-dry for one hour at 150 degrees.

5 On china over 1/16" in thickness, the rivet method is used to stop vibrations because it is necessary to grind a groove only on one side of the article. The groove should be ground on the side that shows least. On a plate, this will be the underside; on a cup, the inside. On an article that has decorations of flowers, etc., on one side where the rivet is to be installed, the groove should be ground in on the undecorated side. The rule is: Save all decorations where possible. The rivet method follows:

  1. Grind in the rivet groove with a No. 2 wheel, centred with the crack at the rim. The first cut should be made directly into the crack on the side where the rivet is to be installed. This grinding is done before cementing a loose crack.
  2. If the crack is loose, the cementing is done next. If the crack is tight, cementing is not necessary.
  3. After the cement has dried and been heated, or for a tight crack, the groove is filled in with pewter.
  4. Smooth off any excess pewter until it is even with the surrounding surfaces, using the hard carbide rubber wheel in the hand grinder. Wash the rivet with soap and hot water, and air-dry for at least one hour. Then give the rivet a coat of No. 100 cement. Air-dry for three hours or force-dry one hour at 150 degrees.

6 If you intend to decorate a repaired crack to make it invisible, follow these preparation steps:

If the crack is very slight and tight, and appears to be just through, or not quite through the glaze or surface, and the fingernail test reveals no crack or uneven edges, it does not need grinding or other preparation. However, if either type of rivet was installed at the rim, it will have to be finished.

Step sequence for prepairing cracks *

  1. Inspect the crack and determine whether it is loose or tight.
  2. * Where a butterfly rivet, or the rivet method is to be used, grind in the grooves.
  3. * Where a crack is loose, do the cementing with the type of cement.
  4. * Dry the cement and heat the pieces.
  5. * Where a groove has been ground in on the rim, fill it with pewter.
  6. * Remove excess pewter from surface of any rivet until it is even with the surface of the article; wash the rivet and give it a coat of No. 100 cement.
  7. * Remove any excess cement from surface of article.
  8. * Where cracks have been cemented, or there are uncemented tight cracks, and the crack needs to be decorated to make it invisible, grind a shallow groove along the edge.
  9. * Where No. 53 mixture is to be used as the filler substance, give the ground surface a coat of No. 100 cement and air-dry.
  10. * Mix the filler substance, fill in and level the rough surface, and dry the mixture.
  11. * Sand dry mixture smooth and even with the surrounding surface.
  12. * Where No. 53 mixture is used to fill the rough surface, give the sanded mixture a coat of No. 53 neutralizer.
  13. * Size the filler substance with proper sizing liquid and give final sanding.
  14. * Frisket any decorations that need protection.
  15. * Decorate the repair.
  16. * Apply the glaze.
  17. * Gold work is applied as the last step.

° Numbers marked with an asterisk may or may not be necessary, depending on the nature of the repair or of the article

Restoring china

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