Are there any solvents, tapes, or methods?

I would suggest starting with a commercal paint stripper available at any home center like Home Depot or Lowes I also found the following site that might help Good Luck !

Care and Cleaning of Art Pottery

There are several simple steps that can be taken to bring out the best in your art pottery and ensure that you are able to display your pottery in its original beauty. Many times we buy collections or individual pieces that have been poorly stored and have more dirt, grime and stains than we would prefer. In an effort to bring these pots back to their original beauty we have experimented with countless cleaning methods with mixed results. The following is a summary of methods we have either tried or heard of being used successfully to clean antique art pottery.

Please use any of these methods at your own risk as all pottery and associated dirt, grime and stains are different. What works in one case may not be at all effective in another and may in fact result in damage to your item.

Cleaning dirt and grime from antique art pottery:

Soak the vase for at least 24 hours in hot water and ammonia mixture. Typically a cup of ammonia can be used per 2 gallons of water. Some people have reported additional success by adding **** and Span to the ammonia/water mixture.

Removing silver or pencil marks from antique art pottery:

The best thing we have found to remove silver or pencil marks from Van Briggle, Rookwood, Roseville, Teco and other matte glazed art pottery is metal polish. We have tried many different brands and while none of the products will work on all marks, we have found Noxon to consistently be the most effective on art pottery. The only place we have found Noxon is at Menards.

To use metal polish to remove marks from your art pottery, simply put a little bit of the Noxon on a rag and rub the silver marks. The rubbing process does typically take a considerable amount of elbow grease but is definitely worth the effort in bringing your art pottery back to factory fresh condition. After the silver marks have been removed, use the clean part of the rag and buff the remaining polish off the vase.

Other methods that are somewhat effective in removing silver or pencil marks from art pottery include: “Barkeeper’s Friend” with a sponge and warm water and using a pencil eraser to attempt to erase the marks off the art pottery.

Removing mineral deposits from antique art pottery:

The most effective thing we have found to remove mineral deposits such as calcium, lime, and rust stains from art pottery such as Roseville, Van Briggle, Rookwood, Weller, and others is to soak the vase in full strength white vinegar.

For lighter mineral deposit staining a day or two of soaking the item in the vinegar is all that is necessary to the remove the mineral deposits. On art pottery that has extensive mineral deposit deposition extended soaking may be required. At times the extended soaking may take weeks to remove the deposits from your art pottery. On art pottery requiring extended soaking to remove lime or calcium buildup we often rub the problem deposits daily with a butter knife to breakup the deposits and thus allow the vinegar to better penetrate the buildup. For extended soaking, we also change the vinegar regularly. Obviously if doing this you must be very careful to avoid damage to your art pottery item.

After you have got the pottery as clean as you can, wash the vase with soap and warm water. You will then need to soak your art pottery in tap water until the vinegar smell is gone.

Other methods, which we have not personally used but have heard to be successful in removing minerals deposits from art pottery, include Lime Away, CLR, and baking soda and water mixture. Obviously, the risk of damaging the finish glaze greatly increases as the harshness of the chemicals you use increases. So proceed with caution and use any of these methods at your own risk.

Removing darkened crazing from antique art pottery:

Hydrogen peroxide can typically be used to lighten darkened crazing on Roseville, Rookwood, Van Briggle, Weller, and other glazed art pottery. Over the years we have heard of numerous techniques for using peroxide to effectively lighten darkened crazing. In general, the procedures that are most reported to be successful go something like this.

Use only 40% hydrogen peroxide and do not dilute. The lightening process will not be successful if you use a lesser strength solution. Be sure to use waterproof gloves and protect all exposed skin. Soak the pottery vase in the peroxide solution. We typically use a small container that can be sealed. Others have reported success with soaking clean rags in peroxide and wrapping the vase in the rags and then placing the vase in a large, sealed baggy.

The process can take weeks and even months in some cases. Since the peroxide loses it’s strength over time if it is exposed to the air, it is important to use a sealed container and to change the mixture from time to time. If using cloths in the baggy, re-soaking them every few days should be sufficient. Periodically check the pottery item to see if the crazing lightened to a satisfactory point; if not continue soaking.

Removing glue and sticker marks from antique art pottery:

We have found De-Solv-it spray to be very effective in removing old sticker stains, glue and related marks on Roseville, Van Briggle, Rookwood, Weller and other glazed art pottery. Typically you can just spray the De-Solv-it on a clean rag and rub on the problem area on the pottery and buff clean with a soft cloth. We have also effectively used acetone on a cloth to remove stickers and glue from art pottery but acetone may damage any repairs on your pottery so be careful if you are unsure if your piece has been repaired.

Removing paint specs from antique art pottery:

Many times when we purchase art pottery items in addition to the dirt and grime accumulated over the years they come with extra drops of paint. Acetone is very effective at removing these paint specs from Roseville, Rookwood, Weller, Van Briggle, Teco and other glazed art pottery. For thicker and aged paint specs you sometimes need to use a safety pin or needle scuff or flake the paint to allow the acetone to work into the paint.