Labels that are difficult to remove can be soaked in hot, soapy water. A good soak for a few hours or overnight should make the labels easier to peel off. [1] X Research source You’ll also have to remove any glue that remains from the label. After a soak in hot, soapy water, you can usually scrape the glue off without much ado. A tool like a putty knife, wallpaper scraper, or an unwanted credit card can help. If your bottles have labels that appear painted, like Corona or Belvedere bottles, you can melt your bottle with these still in place. However, after melting, those labels will be permanently melted to your bottle. [2] X Research source

While you’re cleaning you’ll have a perfect chance to give your kiln a quick safety inspection. Tighten any screws that seem loose, remove any flammable material from around your kiln, and verify that all kiln equipment is in good working order.

Set your kiln to run the appropriate test setting, which will be a medium speed 04 ConeFire program if you are using an 04 cone. Allow the program to run for the complete time indicated. After the program has run and your kiln sufficiently cooled, take a look at your cones or testing material. If using a Witness Cone, you should notice a 20° bend or greater in the cone, with no cones hanging lower than the shelf. If you used other testing materials, check your manual to learn how to understand the results of your test. If after running the ConeFire program none of your cones have bent, this may be an indication that your heating element or a relay may have decayed. In this case, you may need to call a professional, like a kiln technician, to get your kiln back in working order. [4] X Research source

An alternative you might use in place of a kiln wash is special kiln resistant paper, like thin-fire or fiber paper. These will also prevent your glass from melting to your kiln or molds. [5] X Research source

You can also choose a hybrid of these two techniques. Glass slump molds are available at some art/ceramics stores and online. Using these, you can slump your glass into the approximate shape of a mold. This is great for making spoon holders, shallow bowls, and vases. [6] X Research source

Different kinds of glass are made by different chemical processes. Some kinds of glass will react better to one firing profile better than another, so you may have to experiment before you find the best profile for your glass melting. [7] X Research source Many firing profiles are available free online, though some may have come with the manual of your kiln. In some cases, the firing profile recommended by your kiln manufacturer might not produce good results. In this case, you’ll have to tweak your profile. [8] X Research source

If you are using a mold, it should surround your bottle or be positioned in a way that your bottle fills the mold as it melts. The best positioning will depend entirely on the kind of kiln you are using. [9] X Research source

As your kiln achieves the temperature indicated in each segment of your firing profile, you should hold that temperature for however long indicated in the profile. This is usually a short period of time, around 10 - 12 minutes in many cases. You should always wear the appropriate safety gear recommended by your kiln manual when operating your kiln. In many cases this will include heat resistant gloves and safety googles.

The hold time, at this point, will be a little longer than preceding hold times. This longer hold time gives the temperature a chance to equalize.

Once your kiln is at the peak temperature in your firing profile, you should allow for a hold time of about 10 minutes. Slight variations in hold time and temperature will influence the how much your bottle melts. [11] X Research source

Once the inside of your kiln has reached room temperature, you can open it and remove your glass. Be careful when doing so, as the glass may still be hot to the touch. Opening your kiln before it has naturally cooled to room temperature may cause thermal shock. This could cause your glass to crack or shatter. [13] X Research source

Once the bottle begins to slump, it will lose its roundness and rolling will no longer be an issue. Until then, your frit should keep your bottle in place. [14] X Research source

You can also blunt sharp edges by decreasing your hold time. Shorten the time by 5 minutes or less in your future firings. If the sharp edges remain, continue to decrease the hold time in this fashion. In some cases, you may have the best results by lowering your temperature and shortening your hold time. You’ll have to experiment to find what works best for the glass and kiln you are using. [15] X Research source

Alternatively, instead of melting old glass bottles and jars you can use them for organization. [17] X Research source Keep them in your bathroom to organize lipsticks, hair ties, and other things. [18] X Research source Or use them to manage all your office supplies. [19] X Research source